Wikipedia
Zasławski
Zasławski (plural Zasławscy) is a surname of Polish– Ruthenian nobility and a cadet branch of the Ostrogski family. The Zasławski family had its power base in Volhynia, Crown of the Kingdom of Poland (today in Ukraine), and traced its origins to a branch of the Rurikids that took a name from the Iziaslav. Due to their relation to the Rurikids, they held title of Knyaz (Prince).