Theodore was released in 1237 when his daughter Irene married John Asen II, and quickly managed to regain control of Thessalonica, ousting Manuel. Having been blinded during his captivity and thus disqualified from occupying the throne again, he installed his eldest son John as emperor, but remained the "de facto" regent of the state. Manuel tried to regain Thessalonica with Nicaean support, but a negotiated settlement was reached which gave him Thessaly and left Thessalonica and its environs to Theodore and John. In 1241, John III Vatatzes invited Theodore to visit Nicaea. He was welcomed and treated with great honour, but was effectively detained there until the spring of next year, when Vatatzes marched on Thessalonica with Theodore in tow. Theodore was sent in to negotiate with his son and convince him to accept demotion to the rank of Despot and to recognize the suzerainty of Nicaea. John died in 1244 and was succeeded by Theodore's younger son Demetrios. In 1246, Vatatzes overthrew the unpopular Demetrios and annexed Thessalonica. Theodore influenced his nephew Michael II to launch an attack on Thessalonica in 1251, but in 1252, Vatatzes campaigned against them and forced Michael to come to terms. Theodore was taken prisoner and sent into exile in Nicaea, where he died around 1253.