Son of King Alfonso VIII of Castile and Eleanor Plantagenet. Paternal grandson of King Sancho III of Castile and Blanca Ramírez of Navarre. Maternal grandson of King Henry II of England and Eleanor, Duchess of Aquitaine.
He was the eldest son born to Alfonso VIII and his wife Eleanor. From his birth, he was heir to the Castilian throne, but sadly died at the age of three months.