However, soon after his release, William broke his oath of allegiance, and begun seeking alliances with and help from various Western nations. Informed by the local Byzantine governor of William's actions, Michael VIII sent an army under the command of his half-brother, Constantine, against William, but the expedition was unsuccessful, the Byzantines first being routed at the Battle of Prinitza in 1263 and then, after Constantine's return to Constantinople, suffering a heavy defeat at the Battle of Makryplagi in 1264.