Prince Wilhelm Karl of Prussia (Wilhelm Karl Adalbert Erich Detloff; 30 January 1922, in Potsdam – 9 April 2007, in Holzminden) was the third son of Prince Oskar of Prussia, and the last surviving grandson of Wilhelm II, the last German Emperor.
He was the thirty-sixth Master of Knights (Herrenmeister) of the Protestant (and largely German) Order of Saint John (Bailiwick of Brandenburg), also known as Der Johanniterorden.