Dečanski generally maintained an alliance with Andronikos II, aside from occasional disruptions. He avoided taking a position in the Byzantine civil war between Andronikos II and Andronikos III Palaiologos. Nevertheless, as Andronikos III gained control, he developed an alliance with Tsar Michael Asen III of Bulgaria. Michael Asen III divorced Dečanski's sister Anna and married the Byzantine princess Theodora Palaiologina instead. The allies intended to join forces for a major invasion of Serbia in 1330. In the most significant event of Dečanski's reign, he defeated and killed Michael Asen III in the Battle of Velbazhd (1330). Prince Stefan Dušan also contributed to the victory.