Istvan III again took Sirmion & attacked Zeugminon, having Istvan IV murdered

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 
Emperor Manuel I Komnenos (Manuel 1)
  • When Stephanos 53 again took Sirmion and threatened Zeugminon, he sent him a letter threatening to repeat his successes against Geza; when Stephanos ignored it, he prepared for war, thinking of again using Stephanos 54 (:) Kinnamos 231.6-232.3
István III, king of Hungary (Stephanos 53)
  • Again took Sirmion from the Byzantines, threatening Zeugminon; received a letter from Manuel 1 threatening revenge for his breaking of oaths, but was not intimidated; Manuel then prepared for war (:) Kinnamos 231.6-232.3
István IV, king of Hungary (Stephanos 54)
  • The repeated offences of Stephanos 53 against Byzantium made Manuel 1 think again of placing him on the throne, though he had abandoned this plan (:) Kinnamos 231.21-232.3
  • He was eventually murdered by Stephanos 53 and his other Hungarian enemies, who found that Thomas 119 in Zeugminon was willing to kill him; his wound was poisoned as he was being bled (:) Niketas Choniates, Historia 128.4-20
Thomas, attendant of Istvan IV of Hungary, who poisoned him (Thomas 119)
  • Enemies of Stephanos 54, led by Stephanos 53, looked for a way of killing him: they found that Thomas in Zeugminon was willing to do the deed, and fixed a price; when Stephanos 54 was being bled, Thomas poisoned the bandage placed on the wound; the poison spread through his body and he died (:) Niketas Choniates, Historia 128.6-20