João, was a son of king Peter I of Portugal and Galician lady Inês de Castro, "the Queen who ruled after her death".

His father, Infante John, Duke of Valencia de Campos, had been legitimized as Infant of Portugal, and became duke of Valencia de Campos in Castile through his marriage to one of the bastards of King Henry II of Castile.

Fernando's father John, had married in 1376, (1st marriage), Portuguese lady Maria Téllez de Menezes, assassinated shortly after in 1378 by her husband, who had been alerted of her apparent unfaithfulness.

He was the 1st Lord of Eza in Galicia, from where he took his surname, corrupted in Portuguese into Eça, and which was given to him by Fadrique de Castilla, 1st Duke of Arjona who died in prison.

In the end of his life he repented and started wearing a rope of the Habit of Saint Francis of Assisi, with which he was buried and which appears in the coat of arms of his family in purple with the look of a carbuncule.