boris ii of bulgaria was an emperor (tsar) of bulgaria. he was emperor from 969 to 971. his father was peter i of bulgaria. when peter died in 969, his son boris was being held in constantinople by the byzantine emperor nicephorus ii. the byzantines apparently allowed boris to return to bulgaria. when he arrived he was immediately proclaimed tzar boris ii. sviatoslav i of kiev, who had earlier subdued parts of bulgaria, returned in august 969 and subdued the remaining parts of bulgaria. he allied himself to boris ii in order to get his bulgarian soldiers to fight against the byzantines. the new byzantine emperor, john i tzimisces invaded bulgaria. by the end of 971 all of bulgaria was in byzantine hands. by that time boris ii had abdicated.