the first link given by Benjamin stated that he was the Cousin of King Juan Carlos and... Duke of Aquitaine (title associated with monarchists royalist French)
yes, here it is Eric:
Since Gonzalo's mother was not born a princess of a royal house, his grandfather Alfonso XIII did not consider Gonzalo in line to the Spanish throne in accordance with the Pragmatic Sanction of 1776. Gonzalo's father Jaime disagreed, however, and maintained that his sons were Spanish dynasts with the style His Royal Highness. In Spain Gonzalo was generally addressed as Don Gonzalo de Borbón y Dampierre. Elsewhere he was often addressed as a prince with the style His Royal Highness.
The internal family conflict over Gonzalo's rank and title continued throughout his life. In 1972 his uncle the Count of Barcelona invited him to the wedding of his daughter Margarita; the invitation did not recognise the royal rank of Gonzalo who wrote a letter of protest to his uncle.[11]
Gonzalo was considered a French prince with the style His Royal Highness by those legitimists who believed that his grandfather Alfonso XIII was also the heir to the French throne. After his grandfather's death and the accession of his father Jaime in 1941, Gonzalo was regarded as second in line to the legitimist French throne for many years until the birth of his nephew in 1972.
On 8 March 1972, Jaime named him and received him into the Order of the Holy Spirit and the Order of Saint Michael; the declarative letters patent were dated 21 September 1972.[12] Also on 21 September 1972 Jaime gave Gonzalo the title duc d'Aquitaine (Duke of Aquitaine).[13] He was given the Grand Cross of the Order of Saints Maurice and Lazarus by Prince Vittorio Emanuele of Savoy; the document of investiture referred to him as Duke of Aquitaine.
On 14 September 1988, the tribunal d'instance in Montpellier issued a certificate of French nationality to Gonzalo on the grounds that his mother was born French and had retained her nationality when she married. On 18 May 1989, Gonzalo was issued French national identity papers with the name SAR de Bourbon, duc d’Aquitaine, Gonzalve Victor (H.R.H. of Bourbon, Duke of Aquitaine, Gonzalve Victor). He later received a French passport with the same name.
