Constantine was born sometime after 1358 into the family of Bagrat I, then duke (and ex-king) of Imereti, and his wife, a Jaqeli noblewoman of Samtskhe. He was a younger brother of two successive kings of Imereti, Alexander I and George I, who had broken away from the Kingdom of Georgia during Timur's invasions of that country. After the death of George I in the battle with Vameq I Dadiani, Duke of Mingrelia, in 1392, Constantine and his nephew, Demetrius, son of Alexander, fled to the Caucasian mountains, while Imereti was reintegrated by George VII of Georgia.