John VI Kantakouzenos
In 1341–1347, the Byzantine Empire was plunged into a second protracted civil war, between the regency for Emperor John V Palaiologos and his intended guardian John VI Kantakouzenos. The neighbors of the Byzantines took advantage of the civil war, and while Stefan Dušan sided with John VI Kantakouzenos, Ivan Alexander backed John V Palaiologos and his regency. Although the two Balkan rulers picked opposite sides in the Byzantine civil war, they maintained their alliance with each other. As the price for Ivan Alexander's support, the regency for John V Palaiologos ceded him the city of Philippopolis (Plovdiv) and nine important fortresses in the Rhodope Mountains in 1344.