When the Lazarević brothers were in Constantinople, they entered an open conflict with the Branković family. Đurađ Branković was imprisoned at the city dungeon on his return to Constantinople, on Stefan's command. The reason for this is unknown, and many later chroniclers, such as Mavro Orbini, claim that Đurađ was planning to join Bayezid I's son Süleyman, who established his power in the European part of the Ottoman Empire. This is probably true, as Đurađ after escaping from prison in September, went to Süleyman and asked him for military aid against Lazarević.