[1] 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.

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.

Despite conflicting historical details regarding the span and size of the revolt, there are hints that Constantine and Fruzhin managed to restore their rule over at least a part of the Bulgarian lands.

Sigismund rewarded Fruzhin's military service with a noble title, entrusting him with the governance of Temes County and presenting him with a personal domain at Lippa.

[1] An Ottoman register of 1454/1455 mentions Fruzhin as being active in the area between Svrljig and Pirot, having been granted special permission by local authorities to hire men to secure mountain passes there.