There was peace between the Palaiologans and the Ottomans until 1421, when Mehmed I died and Manuel retired from state affairs, to pursue scholarly and religious interests. Manuel's son, John VIII Palaiologos, co-emperor since before 1416, ignored the fragile peace with the Ottomans and supported Mustafa Çelebi, a pretender to the Ottoman throne, in a rebellion against Mehmed I's successor Murad II. Murad defeated Mustafa's rebellion and besieged Constantinople in 1422, though the Byzantines successfully repulsed him. Even during the final decades of the Byzantine Empire, the Palaiologoi often found it difficult to cooperate with each other. During Manuel II's reign, John VIII and the younger son Constantine appear to have got on well with each other, but the relations between Constantine and the younger brothers Demetrios and Thomas were not as friendly.