Son of Philip II. of Spain, born at Valladolid, and heir to the throne, but from incapacity, or worse, excluded by his father from all share in the government; confessed to a priest a design to assassinate some one, believed to be his father; was seized, tried, and convicted, though sentence against him was never pronounced; died shortly after; the story of Don Carlos has formed the subject of tragedies, especially one by Schiller, the German poet (1545-1568).