In 765 the Byzantines again successfully invaded Bulgaria, during this campaign both Constantine's candidate for the Bulgarian throne, Toktu, and his opponent, Pagan, were killed. Pagan was killed by his own slaves when he sought to evade his Bulgarian enemies by fleeing to Varna, where he wished to defect to the emperor. The cumulative effect of Constantine's repeated offensive campaigns and numerous victories caused considerable instability in Bulgaria, where six monarchs lost their crowns due to their failures in war against Byzantium.