Heraclius Constantine (; ; 3 May 612 – 25 May 641), often enumerated as Constantine III, was one of the shortest reigning sole Byzantine emperors, ruling for three months in 641. He was the eldest son of Emperor Heraclius and his first wife Fabia Eudokia.
Reign
Constantine was crowned co-emperor by his father on 22 January 613 and shortly after was betrothed to his cousin, Gregoria, a daughter of his father's first cousin, Nicetas. As the couple were second cousins, the marriage was technically incestuous, but this consideration must have been outweighed by the advantages of the match to the family as a whole. Furthermore, its illegality paled into insignificance beside Heraclius' marriage to his niece Martina the same year. In comparison, Constantine's marriage was far less scandalous than that of his father. Constantine assumed an honorary consulship on 1 January 632, and at the same ceremony his brother Heraclonas was raised to the rank of Caesar.