Soon after Mehmed began his reign, his brother Mustafa Çelebi, who had originally been captured along with their father Bayezid I during the Battle of Ankara and held captive in Samarkand, hiding in Anatolia during the Interregnum, reemerged and asked Mehmed to partition the empire with him. Mehmed refused and met Mustafa's forces in battle, easily defeating them. Mustafa escaped to the Byzantine city of Thessaloniki, but after an agreement with Mehmed, the Byzantine emperor Manuel II Palaiologos exiled Mustafa to the island of Lemnos.