Through most of John VIII's reign, Constantine and Thomas ruled as Despots of the Morea, with Demetrios governing a stretch of land in Thrace. Demetrios was unhappy with his subordinate position and assaulted Constantinople in 1442, with Ottoman help, in an attempt to seize the city and become emperor himself. John VIII, aided by Constantine, successfully repulsed this attack and Demetrios was briefly imprisoned as punishment. After John VIII's death in June 1448, the candidates for the throne were brothers Constantine, Demetrios and Thomas. To avoid infighting, their mother Helena Dragaš decided that Constantine was to be the next emperor. Constantine XI Palaiologos's rise to the throne was also accepted by Murad II, who by now had to be consulted for any appointments.