 Disputes between John V's mother Anna of Savoy and the Patriarch John XIV on one side and Andronikos III's friend and "megas domestikos" John Kantakouzenos on the other led to a new and devastating civil war, lasting until 1347 and won by John Kantakouzenos, who became senior co-emperor as John VI.The weakening of Byzantium as a result of the civil war allowed Stefan Dušan of Serbia to invade Macedonia, Thessaly and Epirus in 1346–1348, creating the Serbian Empire.In the meantime, John VI Kantakouzenos attempted to consolidate his own dynasty on the imperial throne, marrying his daughter Helena to John V and proclaiming his son Matthew Kantakouzenos as co-emperor.