John III Doukas Vatatzes
In 1239, the deposed Manuel returned with Nicaean help and made himself master of Thessaly. Unable to dislodge him, Theodore and John came to terms with the loss of that province. In 1241 Ivan Asen II died, removing both his suzerainty and his protection from Thessalonica. Now, if not earlier, John began using the imperial title once used by his father. This and his exposed position attracted the attention of Emperor John III Doukas Vatatzes of Nicaea. The Nicaean emperor invited Theodore to a conference and had him arrested, and in 1242 led his army against Thessalonica. Upon reaching Thessalonica, he sent Theodore to negotiate with his son and obtain his submission. John was easily induced to content himself with the title of despotes and to recognize the suzerainty of Nicaea. Securing these concessions, John III Doukas Vatatzes rapidly returned to Asia Minor to combat the invading Seljuk Turks.