There is an earlier Sixtus of Bourbon-Parma who was a Belgian army officer in the First World War.
Prince Sixtus Henry of Bourbon-Parma (Spanish: Don Sixto Enrique de Borbón-Parma y Borbón-Busset; Italian: Sisto Enrico di Borbone Parma; born 22 July 1940) is considered Regent of Spain by some Carlists who accord him the titles Duke of Aranjuez, Infante of Spain, and Standard-bearer of Tradition.