After giving the impression that he wished to negotiate, Ivan Alexander, reinforced by Mongol cavalry, overwhelmed the smaller but better organized Byzantine army in the Battle of Rusokastro. The contested cities surrendered to Ivan Alexander, while Andronikos III sought refuge within the walls of Rusokastro. The war ended with Ivan Alexander meeting Andronikos and agreeing a peace based on the "status quo". To seal the alliance, he betrothed his eldest son, Michael Asen IV, to Andronikos's daughter Maria (Eirene), the marriage eventually taking place in 1339. The Bulgarian emperor was now free to turn his attentions to Belaur, but it was not until 1336 or 1337 that the rebellion in the northwest was put down.