Archduke Karl Pius of Austria, Prince Royal of Hungary and Bohemia, Prince of Tuscany (4 December 1909 – 24 December 1953), known as Carlos Pío de Habsburgo-Lorena y de Borbón in Spanish, was a member of the Tuscan branch of the Imperial House of Habsburg and a Carlist claimant to the throne of Spain under the assumed name of "Carlos VIII".

He was the tenth and youngest child of Archduke Leopold Salvator of Austria, Prince of Tuscany and Infanta Blanca of Spain.

Karl was born in Vienna, Austria-Hungary, the youngest son of Archduke Leopold Salvator of Austria (1863–1931) and of his wife Infanta Blanca of Spain (1868–1949).

Karl was given the baptismal names Carolus Pius Maria Adelgonda Blanka Leopoldus Ignatius Raphael Michael Salvator Chrillus Angelus Barbara.

In 1932 a section of the Carlist movement, called cruzadistas from the name of the magazine El Cruzado Español, began to entrust their hopes for the future of Carlism to the sons of Blanca de Borbón.

At the time the Carlist claimant Infante Alfonso Carlos, Duke of San Jaime, Karl's great-uncle, was in his eighties and childless.

Since the cruzadistas believed that there were no more male members of the House of Bourbon eligible to succeed to the Spanish throne, they held that the Carlist claim should pass at the death of Alfonso Carlos to the sons of his closest female relative, Blanca de Borbón y Borbón-Parma.

Several funeral masses were celebrated for him, including one on 16 January 1954 in Madrid, attended by numerous government officials and members of the diplomatic corps.