Duchy of Prussia
After the Polish–Teutonic War (1519–1521), the Order was completely ousted from Prussia when Grand Master Albert of Brandenburg converted to Lutheranism in 1525. He secularized the Order's remaining Prussian territories and assumed from his uncle Sigismund I the Old, King of Poland, the hereditary rights to the Duchy of Prussia as a vassal of the Polish Crown, the Prussian Homage. The Protestant Duchy of Prussia was thus a fief of Catholic Poland.