John III Doukas Vatatzes
John III Doukas Vatatzes, Emperor of Nicaea, invaded Bulgaria soon after Kaliman's death. He captured Serres and seized Melnik with the support of the local inhabitants. He soon invaded the valley of the river Vardar, and occupied all fortresses in the region. Michael II Komnenos Doukas, ruler of Epirus, also broke into Bulgaria and occupied western Macedonia. The Bulgarians acknowledged Vatatzes's conquest in a peace treaty in late 1246 or in early 1247. The treaty also prescribed them to support Vatatzes against the Latin Empire of Constantinople.