Tieran killed the Autarch in front of Ameron. Tieran then transferred his consciousness to Kes since his body was dying. Tieran tried to persuade Ameron to support him against Ameron's older brother Demmas, who was the legitimate heir to the throne. Ameron, an ambitious and jealous young man, agreed to support Tieran, probably to save his own life and to rule beside the tyrant Tieran. Tieran also announced his engagement to marry Ameron in order to legitimize his claim to the throne.
During the rescue attempt of Kes, Tieran transferred his consciousness to Ameron. Kes was able to drive Tieran from Ameron using a device The Doctor had created, and Tieran's consciousness was destroyed. (VOY: "Warlord")