Don Carlos, Imbalanced Heir to Spanish Throne Dies: 1568 AD

Don Carlos died in 1568.  Who was this fellow?  He was heir to the Spanish throne and apparently was severely mentally challenged due to massive inbreeding in the Habsburg dynasty.  He had only 4 great- grandparents (most people have 8), only 6 great-great-grandparents (most people have 16).  Two of his great-grandmothers were sisters.  Sounds like some folks I know down in the American South…