On 21 May 1455 in Córdoba, she married as his second wife King Henry IV of Castile who had repudiated his first consort, Blanche II of Navarre, after thirteen years of marriage. It was rumoured that their marriage had never been consummated due to the king's impotence. Henry and Joan shared the same maternal grandparents; Ferdinand I of Aragon and Eleanor of Alburquerque (making them first cousins). They also shared the same paternal great-grandfather; John of Gaunt, 1st Duke of Lancaster (making them second cousins). In February 1462, six years after Joan's marriage to Henry, she gave birth to a daughter, also named Joan, called "La Beltraneja" because of rumours that she was in fact the daughter of Don Beltrán de la Cueva, 1st Duke of Alburquerque, who was suspected of being Joan's lover.