During the Protestant Reformation, endemic religious upheavals and wars occurred across the region. In 1525, during the aftermath of the Polish-Teutonic War (1519–1521), Sigismund I the Old, King of Poland, and his nephew, the last Grand Master of the Teutonic Knights, Albert of Brandenburg-Ansbach, a member of a cadet branch of the House of Hohenzollern, agreed that the latter would resign his position, adopt Lutheran faith and assume the title of Duke of Prussia. Thereafter referred to as "Ducal Prussia" (; ), remaining a Polish fief.