After 1328 Andronikos III won and deposed his grandfather. Serbia and the Byzantines entered a period of bad relations, closer to the state of undeclared war. Previously, in 1324, he divorced and ousted his wife and Stefan's sister Anna Neda, and married Andronikos III's sister Theodora. During that time the Serbs captured some important towns such as Prosek and Prilep and even besieged Ohrid (1329).

Both Empires(Byzantine and Bulgarian) were seriously worried about the fast growth of Serbia and on 13 May 1327 settled a clearly anti-Serb peace treaty. After another meeting with Andronikos III in 1329, the rulers decided to invade their common enemy; Michael Asen III prepared for joint military operations against Serbia. The plan included the thorough elimination of Serbia and its partition between Bulgaria and the Byzantine Empire. 

The bulk of the two armies camped in the vicinity of Velbazhd, but both Michael Shishman and Stefan Dečanski expected reinforcements and from 24 July they began negotiations which ended with a one-day truce. The Emperor had other problems which influenced his decision for the truce: the army supply units had not yet arrived and the Bulgarians were short on food. Their troops scattered around the country and the nearby villages to search for provisions. Meanwhile, receiving a sizable reinforcement, 1,000 heavily armed Catalan horsemen mercenaries, led by his son Stefan Dušan during the night, the Serbs broke their word and attacked the Bulgarian army. early on 28 July 1330 and caught the Bulgarian army by surprise. The Serbian victory shaped the balance of power in Balkans for the next two decades.