When Istvan III again took Sirmion from the Byzantines and threatened Zeugminon, Manuel I sent him a letter threatening to avenge his breaking of oaths by repeating the successes he had achieved against Geza II. When the king ignored the letter and besieged Zeugminon, Manuel prepared for war. The constant offences of Istvan III made the emperor think again of putting Istvan IV on the throne, a policy he had abandoned. Istvan III and other Hungarian opponents of Istvan IV decided to put a stop to the years of warfare he had caused. They enquired for somebody in Zeugminon, where he was under siege, to poison him, and found Thomas, one of his attendants, unprincipled enough to take money to murder his master. When the ex-king was being bled, he soaked in poison the bandage which was placed on the wound. The poison spread throughout his body and he died