"The Two Sicilies royal house has been divided for the past fifty-four years by a painful dispute over the succession to the headship of the dynasty. This had its roots in misinterpretations of the succession laws, which originated at a time when the Kingdom of the Two Sicilies was a significant European power. These divisions have now been settled.
Although the Spanish and Two Sicilies succession had been ruled by Salic law from 1714, in 1830 the Spanish was amended to give females a right of succession after their brothers, should the latter have no male issue, enabling Ferdinand VII's elder daughter to succeed him as Queen Isabel II. This did not deprive the male descendants of Philip V of their Spanish rights but placed them in order of succession after any females born of a senior male line. As a result of this amendment all the descendants of King Francis I and his wife, the former Infanta Doña Isabel, acquired a superior right to the Spanish Throne by virtue of their descent from her instead of his father Ferdinand. While this right preceded their existing one as descendants in the male line from Charles III, it also placed them after the descendants of born and unborn Infantas. When in 1901 Prince Don Carlo of the Two Sicilies, second son of the Count of Caserta, married the Infanta Doña Mercedes, then heiress presumptive to the Spanish Throne, the Queen Regent and the Count of Caserta agreed that he should be required to renounce his Italian Nationality on becoming Spanish (which he did on February 7, 1901). The Spanish Government advised the Queen, however, that no renunciation of dynastic rights could be legal or binding.
The Count of Caserta had offered the Collar of Saint Januarius to King Alfonso XIII but was informed (by his sister-in-law, the Infanta Doña Isabel, Countess of Girgenti), that it would be impossible for him to accept any Neapolitan Orders because of the fear of upsetting relations with Italy. Prince Don Carlo himself was told that he could not wear his San Gennaro decorations at the wedding and, unlike his brothers, was never given the Constantinian Bailiffship. Even greater protests were made by liberal deputies in the Spanish Parliament (Cortes) because of the Count of Caserta's role as Chief of the General Staff of the Carlist Armies in the second Carlist war. As such he had been head of an army which had taken up arms against the existing Spanish Monarchy. One leading deputy even demanded that the Count of Caserta be required to publicly disavow both Carlism and his claim to the Neapolitan Throne, because of the possible offense his close relationship with the Crown might cause the new Kingdom of Italy. Carlism being at that time an extremely conservative movement, the fear was expressed that should Prince Don Carlo become King Consort, he would try and reimpose an authoritarian and anti-Constitutional Monarchy. Several deputies signed a petition asking that the Princess of the Asturias be required to renounce her rights to the throne and properties of the family, describing Prince Don Carlo as "Señor Don Carlos de Borbón". When another deputy named him as "Princípe Don Carlos de Borbón", there were protests "prince of where....?".
The Count of Caserta required Prince Don Carlo sign the Act of Cannes in "execution" of the requirements of the Pragmatic Decree of 1759, which required that if the King of Spain or the King of the Two Sicilies inherited both thrones he must renounce the latter to the next Prince in line after the heir apparent. The Spanish government, familiar with the terms of the Pragmatic Decree and the incompatibility of the two Crowns being held by the same person, announced that no renunciation was either necessary or legal in the circumstances then prevailing. The Count of Caserta and the Queen Regent agreed in letters dated 6 and 10 December 1900 that the only renunciation necessary was of nationality.
At the time of the revocation of Salic Law, Francis I of the Two Sicilies wrote to King Ferdinand VII of Spain on March 29, 1830, complaining that this had affected the "rights of my descendants, because it deprived them of the eventual succession to the throne of Spain which they had been assured by the pre-cited law of Philip V". He continued that he desired that his "male posterity would continue to conserve these rights that had been transmitted to them" by Philip V.  He did not apparently see any conflict with being both a Two Sicilies and Spanish dynast. On May 18, 1833, Ferdinand II issued a formal protest against the repeal, declaring that all the descendants of Philip V had been guaranteed their right to the Spanish throne forever, a right that passed "according to the order and rank of their birth .... by primogeniture, following the death of the last possessor of the Crown .... to the line nearest to the deceased and that the succession cannot be designated by the predecessor but by God alone, by the order of succession already established". 
In 1868 a similar situation to the problems over Prince Don Carlo's marriage had arisen over the marriage of his uncle, Prince Don Gaetano of the Two Sicilies, then next in line after the Count of Caserta (at the time heir presumptive to their elder half-brother, Francis II), to the Infanta Doña Isabel, eldest daughter of Queen Isabel II of Spain. The Infanta Doña Isabel had been heiress presumptive to the throne from her birth on December 20, 1851 and, as such, was created Princess of Asturias on March 24, 1852, until the birth of her brother Alfonso (future Alfonso XII) on November 28, 1857. Following her marriage on May 14, 1868, the Count of Girgenti was created an Infante of Spain and there was discussion among his brother's Ministers as to whether he should renounce his Two Sicilies rights. Very properly, and in accordance with Two Sicilies law, it was determined that the Pragmatic Decree of Charles III was still in force and an act was drawn up for his signature requiring him to renounce his Two Sicilies rights in the event that he became King Consort of Spain. After further reflection he never actually signed this act, which remained ready should he succeed as King Consort, and is conserved in the archives of the House.
On September 30, 1868, there was a revolution and Queen Isabel II left for exile in Paris. On June 25, 1870, she abdicated as Queen to her son, Alfonso XII (who was himself living in exile until his proclamation as Constitutional King on December 29, 1874 and reentry into Madrid on January 11, 1875), at which point the Infanta Doña Isabel, Countess of Girgenti, once again became heiress presumptive but without receiving the title of Princess of Asturias. Prince Don Gaetano, a sad and troubled young man, shot and killed himself while staying at the Hotel du Cygne, Lucerne, on November 26, 1871, without leaving issue. His widow, who continued to be styled Countess of Girgenti, survived him to die in exile in Paris on April 23, 1931, nine days after the fall of the Spanish Monarchy.
The subsequent dispute over the succession to the headship of the dynasty followed different interpretations of the act of Cannes of 1900 and it's validity.
King Juan Carlos in 1983 commanded an investigation into the contested succession by five institutions: the Institute "Salazar y Castro" (part of the Superior Institute of Scientific Investigation), the Royal Academy of Jurisprudence and Legislation, the Ministry of Justice, the Ministry of Foreign Affairs and the Council of State. After a detailed examination of the issues, fully described in their reports,  all five bodies reported unanimously to the King that the heir to the Headship of the Royal House of the Two Sicilies and its prerogatives was H.R.H. Don Carlos de Borbón-Dos Sicilias y Borbón-Parma, Duke of Calabria (now also Infante of Spain). On March 8, 1984, this decision was conveyed to H.R.H. in a formal letter from the Head of the Royal Household. The present Infante Duke of Calabria's membership of the Two Sicilies Dynasty was affirmed by the Spanish Government in 1994 when it accorded him the name "Borbón-Dos Sicilias" in the decree creating him an Infante of Spain as the "representative" of a line tied historically to the Spanish Crown.
The act of reconciliation signed on 25 January 2014 now makes any further debate unnecessary as the heads of the two branches of the Royal House have agreed to set aside their differences and recognise each other's titles, while affirming their equality within a united royal house.
 He also succeeded as Xth Grand Master of the Sacred Military Constantinian Order of Saint George.
 Villarreal de Alava, Op. Cit., p. 779.
 For the full text of the debate, see the Reports of the Cortes, Madrid, December 3,6,12,13,15,17,18,19 and 20, 1900. Villarreal de Alava, Op. Cit., pp. 760-781.
 S.A.R. el Príncipe Don Carlos no estaba obligado a renunciar a ninguna clase de derechos familiares ni dinásticos, antes bien, no podia hacer ninguna renuncia de esta especie: en primer lugar, porque los derechos dinásticos son en sí irrenunciables y en segundo lugar porque no existiendo la Corona de las Dos Sicilias, no se podia renunciar a la misma ni con carácter eventual. Informes Emitidos por el Ministerio de Justicia, relativos al Titulo de Jefe de la Casa Real de Borbón Dos Sicilias y al Gran Maestrazgo de la Sagrada Militar Orden Constantiniana de San Jorge, Segunda Parte (D), Madrid, 1987, pp. 54-55.
 The Two Sicilies succession was governed by the Pragmatic Decree of 1759, which required that it pass by male primogeniture. Two Sicilies civil law, in common with the laws of the Kingdom of Italy (of which the Two Sicilies Princes were legally citizens in 1900), and France (where the Act of Cannes was signed), forbade the renunciation of future rights of inheritance, or of name. The Two Sicilies Constitution of 1848 and 1860 did not make any provision for renunciations of future succession rights. Neither was there any provision in Two Sicilies law for the Sovereign to nominate an heir in preference to his successor by male primogeniture. A Prince of the Two Sicilies can only be excluded from the succession if he marries unequally without the prior written permission of the Sovereign (or Head of the Dynasty).
 The unity of the House was emphasized in the Third Family Pact of 1761, with the Headship of the entire House reposing in the person of the King of France, the primogeniture heir. Under the Restoration Monarchy the Almanach Royal placed all the Capetian dynasties, France, Spain, the Two Sicilies and Lucca (Parma) under the words "Maison de Bourbon" and Louis XVIII himself, writing to Paul I of Russia, described himself as "chef de la Maison de Bourbon" (June 24, 1799). In 1808 Ferdinand IV and III protested to Napoleon against the usurpation of the Spanish Throne which directly affected the rights of himself and his descendants. The French Ambassador to Spain, the Vicomte de Saint-Priest, wrote to the Spanish Secretary of State at the time of the Repeal of Salic Law in 1830 using the words "des trois branches de la Maison de Bourbon". The Almanach de Gotha always included all the branches under "Bourbon"; Père Anselme, Histoire de la Maison Royale de France, 9 volumes, 1726-1733, likewise included all the branches together; The Almanach Royal 1720-1830 the same; D. de Araujo Affonso, H. Cuny, A. de Mestas, S. Konarski and H. Pinoteau, Le Sang de Louis XIV, 2 vols, Braga 1961; and Patrick van Kerrebrouck, La Maison de Bourbon 1256-1987, 1987, to name a few of the many.
 Son pero costretto di osservarle, che questo atto ferisce ed anulla i dirittti della suddetta mia discendenza, perché la priva dell'eventuale successione al Trono di Spagna che dalla precitata legge di Filippo V l'era stata assicurata che la mia posterita maschile conserVi indenni quelle ragioni, che dal Nostro augusto bisavolo l'erano sdtato tramandate.. See Villarreal de Alava, Op. cit., pp.707-709. See full text
 Ciascuno secondo l'ordine, el rango di sua nascita, per la morte dell'ultimoo possessore delkla Corona, questa e' deferita di pieno diritto al primogenito del ramo primogeniale, e piú prossimo al defunto, e'l suo successore non la tiene per alcuna disposizione de lprdeccessore, ma da Dio solo, e dalla legge inviolabiler, per la quale l'ordine della successione e' stato stabilito. See Villarreal de Alava, Op. cit., pp. 719-723. See full text.
 There are several examples of members of foreign royal houses who were Infantes of Spain and also members of foreign dynasties and even reigning dynasties. In 1906, Prince Ferdinand of Bavaria married the younger sister of Alfonso XIII and was created an Infante of Spain; he was not required to renounce his Bavarian rights which he transmitted to his sons. Only in 1914 on marrying for the second time, unequally, after the death of his first wife, was he required to renounce his Bavarian rights. Even more relevant was the nomination of four successive Sovereigns of the Bourbon-Parma family as Infantes of Spain: Lodovico I (1773-1803), then heir to Parma and from 1801 King of Etruria, was created an Infante on November 30, 1795; his son and heir, Carlo Lodovico II (1799-1883), King of Etruria (1803-1807), Duke of Lucca (1824-1847) and Duke of Parma (1847-1849), was created an Infante of Spain (by the Carlist claimant, Carlos V) on July 17, 1834; his eldest son and heir, Carlo III (1823-1854), Duke of Parma (1849-1854), was created an Infante of Spain on October 8, 1852, as was his brother, Enrico, Count of Bardi; and the last reigning Duke of Parma, Roberto I (1848-1907), Duke of Parma (1854, deposed 1859), was created an Infante of Spain on May 19, 1854. In none of these cases was the title of Infante of Spain considered an obstacle to these Princes reigning as Sovereigns in Italy.
 The concept of the invalidity of dynastic renunciations may seem strange. It might seem natural that if a prince (or princess) wanted to renounce, he or she should be able to do so. But thrones (and their related prerogatives and titles) are not personal property, the right of succession is not a possession, but something invested in a prince by certain ancient customs or solemn laws. This right carries with it both obligations as well as privileges and these cannot be disposed of at will. Jacques Ellul, in Histoire des institutions, Paris 1956, Vol 2, p. 234, states correctly when speaking of the French Crown that "the king cannot modify the succession by his own volition ... the Crown is not the property of the king. Custom alone rules the succession, and a custom that is such that the laws of the king cannot change nor abrogate it. The law substitutes in place of the deceased Sovereign the person of his eldest son, automatically. ... The king cannot modify the laws of succession...., he cannot abdicate; he cannot designate a successor to the Crown in the case of the lack of a legitimate heir; those able to succeed cannot renounce their rights in advance". This very strict interpretation of the French laws has been modified in the case of Spain and the Two Sicilies, both of whose successions were established not by custom but by solemn laws on the accession of the new dynasty. These laws were instead inviolable and no attempt was ever made to revise the terms of the Pragmatic Decree of 1759 which invested the Throne of the Two Sicilies in the person of the male descendants of Ferdinand IV and III (I) by primogeniture and after him those of his younger brothers.
 In 1962 Prince Ranieri, Duke of Castro, issued a statement published by the Deputation (of which his son, Prince Don Ferdinando, was then President) denying the right of the Count of Barcelona to be Sovereign of the Golden Fleece. Prince Ranieri stated that he would "consign the insignia to his archives" and, on his death, they were not returned to the Count of Barcelona. In 1977 the Count of Barcelona abdicated as Head of the Royal House and Sovereign of the Golden Fleece to King Juan Carlos but the present Duke of Castro has not apparently reversed his father's position on this issue. Bolletino del S.M.O. Costantiniano di San Giorgio, Napoli, Luglio 1962 ( Ranieri Duca di Castro entitolato come Gran Maestro, Principe Don Giovanni di Borbone-Due Sicilie Presidente della Deputazione, pubblicazione della Gran Cancelleria dell'Ordine sotto l'autorizzazione del Duca di Castro ), pp. 73-80.
 Published in English in Sainty, Op. cit. 1989, pp. 134-191.
 The report of the Italian Council of State was concerned with the status of the Constantinian Order and its survival, rather than the disputed succession, which was not mentioned anywhere in the report.
 The Castro side, however, has found wider support in Italy in the past, not least because the post-colonial hostility to Spain on the part of Neapolitans is still pervasive. Some senior officers of the Corpo della Nobiltà Italiana have shown their support for the Castro claim, despite the activities of the Duke of Castro and his son Prince Don Carlos, also styled Duke of Calabria, in promoting a Bourbon Monarchist movement in Southern Italy. There is an obvious conflict with allegiance to H.R.H. Crown Prince Victor Emmanuel of Savoy, who represents the claim to a united Italy, and support for the Duke of Castro and his son since the latter in particular has been most active in promoting the perpetuation of Bourbon Monarchism. Although they have not yet actively advocated the separation of Southern Italy - as have the Party del Nord, for example - there has been a substantial swing on the part of Neapolitan and Sicilian Monarchists against the Savoy dynasty and in favor of the Bourbons which would not have occurred had Prince Ferdinando not given this movement his support. The Neapolitan and Sicilian newspapers give frequent coverage to the activities of Prince Ferdinando and Prince Don Carlo, reporting the cries of "Viva il Re" which sometimes greet them and the public commemorations of the great moments in the history of the Bourbon dynasty in which they participate. In the eyes of many Neapolitans today Prince Ferdinando and his son are the better known representatives of Monarchist sentiments while the Savoy dynasty has been sidelined.