In 1341–1347 the Byzantine Empire was plunged into a protracted civil war between the regency for Emperor John V Palaiologos under Anna of Savoy and his intended guardian John VI Kantakouzenos. The neighbours of the Byzantines took advantage of the civil war, and while Stefan Uroš IV Dušan of Serbia 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. This peaceful turnover constituted the last major success of Ivan Alexander's foreign policy.