DUCAS, emperor of the East, the youngest son of the preceding, succeeded his father Constantine XI. in 1067, together with his brothers Michael and Andronicus, under the regency of their mother Eudoxia, who married Romanus III. Diogenes and made him emperor.
After the capture of Romanus by the Turks in 1071, Constantine and his brothers were proclaimed emperors, but Michael, the eldest, was the real ruler. Constantine was confined in a monastery by the emperor Nicephorus III. Botaniates about 1078. His final fate is not well known.
He died either in the same year in consequence of cruel tortures to which he had been exposed, or as late as 1082, in a battle between the emperor Alexis I. and Robert Guiscard. Anna Comnena calls him Constantius (p. 117, ed. Paris). [MICHAEL VII.; ROMANUS III]