 Complete the following phrase:  Constantine died probably c. 1211. Theodore I, whose children Nikolaos and John died c. 1212, was succeeded in 1222 by his son-in-law, John III Doukas Vatatzes, who had married Irene Laskarina. Vatatzes had to fight off a rival claim by Isaac and Alexios, the brothers of Theodore I, who fled to the Latin Empire and sought aid. Vatatzes 