- Lived 1311-1350. Reigned from the age of one, in 1312, though under the regency of his grandmother, Maria de Molina, till 1325 when he reached his majority.
- Married Maria, daughter of Afonso IV of Portugal, who gave birth to Pedro the Cruel of Castile. Afonso XI's affair with Leonor de Guzmán, despising his own wife, caused much strife in Castile and rivalry for the throne between his two sons, Pedro, his legitimate heir, and Enrique de Trastâmara, Leonor de Guzmán's son.
- Uncle of Fernando, Marquis of Tortosa, son of his sister Leonor of Castile, second wife of Alfonso IV of Aragon. [Pedro, ch. 17: 20-21]
- Alfonso XI of Castile and Afonso IV of Portugal fought in the decisive Battle of the Salado (1340) against the Sultans of Morocco and of Granada.
- Died of the plague at the siege of Gibraltar (1350).