Tradition asserts that her father, Don Pedro Fernandez de Castro, and her mother, Dona Aldonca Soares de Villadares, a noble Portuguese lady, were unmarried, and that Inez and her two brothers were consequently of bastard birth.
Educated at the semi-Oriental provincial court of Juan Manuel, duke of Penafiel, Inez grew up side by side with Costanga, the duke's daughter by a scion of the royal house of Aragon, and her own cousin.
In 1341 the two girls left Penafiel; Costanca's marriage was celebrated in the same year, and the young infanta and her cousin went to reside at Lisbon, or at Coimbra, where Dom Pedro conceived that luckless and furious passion for Inez which has immortalized them.
Pedro's connexion par amours with Inez would of itself have aroused no opposition.
He went in secret to the palace at Coimbra, where Inez and the infante resided, accompanied by his three familiars, and by others who agreed with them.