 In Tmutarakan, Boris was accepted by his cousin, Prince Roman Svyatoslavich.The two were soon joined by Roman's brother, Oleg, who had been banished by his uncles from the Principality of Vladimir.Boris and Oleg allied themselves with the Cumans and attacked Vsevolod on the Sozh River, defeating his army in a bloody battle and capturing Chernigov on 25 August 1078.