Edward the Black Prince compelling Peter of Castile to flee from his kingdom, and in setting up his bastard brother, Henry of Trastámara, as king in his stead. Peter, who was in alliance with Edward III, sent messengers to the Black Prince asking his help, and on receiving a gracious answer at Corunna, set out at once, and arrived at Bayonne with his son and his three daughters. The prince met him at Capbreton, and rode with him to Bordeaux. Many of the prince's lords, both English and Gascon, were unwilling that he should espouse Peter's cause, but he declared that it was not
Edward the Black Prince he was taking into his pay. While his army was assembling he remained at Angoulême, and was there visited by Peter. He then stayed over Christmas at Bordeaux, for his wife, Joan, was there brought to bed of her second son Richard (the next king of England). The Black Prince left Bordeaux early in February 1367, and joined his army at Dax, where he remained three days, and received a reinforcement of four hundred men-at-arms and four hundred archers sent out by his father under his brother John, duke of Lancaster. From Dax the prince advanced via Saint-Jean-Pied-de-Port through Roncesvalles