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
Prince of Wales regard as having been the last native Prince. On 16 September 1400, he was proclaimed Prince of Wales by his supporters, and held parliaments at Harlech Castle and elsewhere during his revolt, which encompassed all of Wales. It was not until 1409 that his revolt in quest of Welsh independence was suppressed by Henry IV. The tradition of conferring the title "Prince of Wales" on the heir apparent of the monarch is usually considered to have begun in 1301, when King Edward I of England invested his son Edward of Caernarfon with the title at a Parliament held in Lincoln.