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 the youngest son of Archduke Leopold Salvator of Austria (1863–1931) and his wife Infanta Blanca of Spain (1868–1949), who were both prominent figures in their own right.