Both Boril of Bulgaria and MichaelI Doukas wanted to expel the Latins from Thessalonica, prompting Emperor Henry to visit the town regularly. Taking advantage of Henry's absence, Theodore sent his fleet to attack Constantinople in the spring of 1211. Boril invaded Thrace, but he could not prevent Henry from returning to his capital. KaykhusrawI and AlexiosIII invaded Nicaea, forcing Theodore's troops to abandon the siege and hurry back to Asia Minor. The two armies met at Antioch on the Maeander in late spring or around 17 June. The Seljuq troops were close to winning the battle, but Theodore sought out Kaykhusraw and killed him in single combat. AlexiosIII was captured during the battle, and Theodore had his father-in-law imprisoned. He concluded a peace treaty with Kaykhushraw's son and successor, Kaykaus I.