After about 1330, she became the long-term mistress and favourite of Alfonso XI,[2] with whom she had the illegitimate son Henry "the Fratricidal", future first monarch of the House of Trastámara.

The humiliated queen resented her unfaithful husband and asked him to cease his public displays of preference for his mistress.

The king ignored his wife's pleas, and gave Eleanor Huelva, Tordesillas, and Medina-Sidonia in addition to other holdings.

The court was increasingly troubled by Alfonso's behavior and as a result, the Pope intervened by forcing Portugal to invade Castile.

Thirsting for revenge, Maria imprisoned Eleanor, and later ordered the execution of her rival in 1351 in the alcázar of Talavera de la Reina.