Before revision: He ruled a or (Grand Duchy), while a ruler of its vassal constituent (udel, udelnoe knyazivstvo or volost) was called udelny knyaz or simply knyaz.
After revision: He ruled (Grand Duchy), while a ruler of its vassal constituent (udel, udelnoe knyazivstvo or volost) was called udelny knyaz or simply knyaz.