During his reign, Petar kept good relations with both the Byzantine emperor Leo VI the Wise (ruled 886-912) and the emperor Simeon I of Bulgaria, second son of late emperor Boris, (893-927). He was connected with Simeon by the peace treaty but also with the custom of "kumstvo". Strains between Bulgarian and Byzantine empires resulted in the Byzantine–Bulgarian war of 894–896, which was continued as the Byzantine–Bulgarian war of 913–927. This affected Serbia a lot. One of the most important moments in this second war was the Battle of Anchialus, held on 20 August 917, when Simeon defeated the Byzantines. Peter apparently leaned on the Byzantine side. Right before the battle, on the bank of the Neretva river, he met with Leo Rhabdouchos, Byzantine strategos of Dyrrachium. Michael Višević, ruler of Zachlumia, who held good personal relations with Simeon, dispatched this to the Bulgarian emperor, accusing Petar of collusion with the Byzantines. He also reported that the Byzantines are bribing Peter in order for him to cooperate with the Hungarians in the joint attack against Bulgaria. This was used by Simeon to start the Bulgarian–Serbian wars of 917–924. Bulgarian army which attacked Serbia was headed by Pavle Branović, son of blinded Bran. Despite that safety was granted to Petar because of his close relations with Simeon, he was captured and sent to Bulgaria where he died imprisoned, while Pavle became the new ruler by the end of 917.