Neither Fruzhin's birthdate nor his biography prior to the Fall of Tarnovo to the Ottomans in 1393 are known, but from his involvement in the 1404 uprising, the former can be narrowed down to the 1380s, the same decade his parents married, and there's no mention of him having been a bastard. He had a brother, Alexander, who converted to Islam after the Ottoman conquest, adopting the name Iskender and becoming governor of Samsun and then Smyrna, where he died in 1418. As the capital Tarnovo was captured by the Ottomans, Fruzhin fled initially to the domains of his uncle Ivan Sratsimir at Vidin, in the Bulgarian northwest.