Vukan Nemanjić, ruler of Zeta, expelled his brother, Stefan, from Serbia in 1202. Kaloyan gave shelter to Stefan and allowed the Cumans to invade Serbia across Bulgaria. He invaded Serbia himself and captured Niš in the summer of 1203. According to Madgearu he also seized Dobromir Chrysos's realm, including its capital at Prosek. Emeric, King of Hungary, who claimed Belgrade, Braničevo and Niš, intervened in the conflict on Vukan's behalf. The Hungarian army occupied territories which were also claimed by Kaloyan.