 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.