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, as his father's successor and his son's predecessor.
Wilhelm-Karl was the youngest of Prince Oskar of Prussia and Countess Ina Marie von Bassewitz's four children.
[1] Having been admitted to the Bailiwick of Brandenburg of the Order of Saint John of the Hospital at Jerusalem (known unofficially as the Johanniterorden, the Protestant successor of the mediaeval Knights Hospitaller) in 1944, he later succeeded his father as its head, serving as the thirty-sixth Herrenmeister ("Master of the Knights") of the Order from 1958 until 1999.
Wilhelm-Karl worked tirelessly[citation needed] to keep the Order intact during the Cold War and helped to reunite its membership after the fall of East Germany.
The couple had two sons and a daughter:[1] This page is a translation of the article in the German language Wikipedia