The life of Constantine is unknown until 1259, when he was appointed "Caesar" by his elder half-brother, Michael VIII. The following year, he was also created a "sebastokrator". He commanded the Byzantine forces on an unsuccessful campaign against the Latin Principality of Achaea, where his army was routed at the Battle of Prinitza. However, Constantine had already left the region by the time of the major Byzantine defeat at the Battle of Makryplagi in 1263/1264.