Princess Zaida of Seville was a refugee Muslim princess who was a mistress and then perhaps queen of Alfonso VI of Castile. She is said by Iberian Muslim sources to have been the daughter-in-law of Al Mutamid, the Muslim King of Seville, wife of his son Abu al Fatah al Ma'Mun, Emir of Cordoba, (d. 1091). Later Iberian Christian chroniclers call her Al Mutamid's daughter, but the Islamic chroniclers are considered more reliable. With the fall of Seville to the Almoravids, she fled to the protection of Alfonso VI of Castile, becoming his mistress, converting to Christianity and taking the baptismal name of Isabel. She was the mother of Alfonso VI of Castile's only son, Sancho, who, though illegitimate, was named his father's heir but was killed in the Battle of Uclés of 1108 during his father's lifetime.