He took part in the battle of Alfarrobeira, where his father's army was defeated by the Portuguese royal army.
He was imprisoned and was to be executed. However, due to the intervention of his aunt Isabella, he was sent into exile in Burgundy together with his brother James and sister Beatrice. His aunt Isabella reigned as Duchess of Burgundy and was able to offer protection to her nephews and niece as wife of Duke Philip the Good. In 1456, John was elected a Knight of the Order of the Golden Fleece.
Raphael de Smedt (Ed.): Les chevaliers de l’ordre de la Toison d’or au XVe siècle. Notices bio-bibliographiques. (Kieler Werkstücke, D 3) Verlag Peter Lang, Frankfurt 2000, ISBN 3-631-36017-7, p. 135f.