John III Doukas Vatatzes
Constantine had six brothers: Manuel Laskaris (died after 1256), Michael Laskaris (died 1261/1271), Georgios Laskaris, Theodore, Alexios Laskaris, and Isaac Laskaris. The last two fought with the Latin Empire against Theodore Laskaris' successor, John III Doukas Vatatzes, and were imprisoned and blinded.