Infanta Blanca of Spain was the eldest child of Infante Carlos, Duke of Madrid, Carlist claimant to the throne of Spain and his wife Princess Margherita of Bourbon-Parma. Blanca was a member of the House of Bourbon and - according to the Carlists - an Infanta of Spain by birth. In 1889 she married Archduke Leopold Salvator of Austria, Prince of Tuscany. The couple had ten children. The family left Austria after the end of the Monarchy and finally settled in Barcelona. When the male line of Blanca's family died out at the death of her uncle, Alfonso Carlos, Duke of San Jaime, some of the Carlists recognized her as the legitimate heiress to the Spanish throne.

Don Carlos de Borbón y Austria-Este was the Carlist claimant to the throne of Spain from 1868, and holder of the Legitimist claim to the throne of France after the death of his father in 1887.