House of Lara
In 1273, being regarded as an expert on military strategy, he accompanied his step-brother, the infante Ferdinand de la Cerda, son and heir of King Alfonso X, to the campaign that began in that year against the Emirate of Granada and against the rebels that had risen up against the King. Amongst others who joined this campaign were the infante Felipe de Castilla y Suabia, brother of the king, and Nuño González de Lara "el bueno", the then head of the House of Lara. In 1274, his father entrusted him with the defence of Sevilla while he pursued the "Fecho del Imperio" or the title of King of the Romans, the throne of the Holy Roman Empire. While Alfonso Fernandez was defending the city against Muslim attacks, the Castillian troops were defeated at the Battle of Écija and the commander of the Christian troops and head of the House of Lara, Nuño González de Lara "the good", was killed during the battle.