Constantine Diogenes (son of Romanos IV)

Constantine Diogenes (died 1073) was one of the sons of Byzantine Emperor Romanos IV Diogenes (reigned 1068–1071).

He was a son of Romanos with his unnamed first wife, a daughter of Alusian of Bulgaria, and hence excluded from the line of succession when his father married the empress-dowager Eudokia Makrembolitissa in 1068. He was named after his grandfather, general Constantine Diogenes (died 1032).

The then kouropalatissa Anna Dalassena (later, regent of he empire), wife of the brother of the late Emperor Isaac I Komnenos, despised the Doukas imperial family. According to perceptions of Anna Dalassena, the Doukas men had usurped the imperial dignity making emperor Isaakios to resign and her husband, the kouropalates Ioannes Komnenos, to refuse the throne. Anna Dalassena expected the Doukas men to lead the country to military problems. Consequently, Anna Dalassena plotted with Romanos Diogenes and others to push the underage Doukas aside. Romanos Diogenes was raised to the imperial throne, having to marry the Doukas dowager empress Eudokia Makrembolitissa. As a signal of strength of the allied supporters and Romanos IV, the marriage of Konstantinos Diogenes was arranged. Emperor Romanos' son received the daughter of kouropalates Ioannes Komnenos and kouropalatissa Anna Dalassena as his bride. The marriage was one of signals of the anti-Doukas camp. He was married to Theodora Komnene, sister of the later emperor Alexios I Komnenos (reigned 1081–1118), some time during his father's reign. Their daughter Anna Diogenissa became the consort of Serbia after her marriage to Uroš I of Serbia.

Constantine fell in battle in 1073. An adventurer pretended to be him in the 1090s, and invaded the Byzantine Empire with Cuman help in 1095.