In 1791 he married Frederica Wilhelmina, daughter of Frederick William II., king of Prussia, thus cementing very closely the relations between the houses of Orange-Nassau and Hohenzollern.
His father was Christian Augustus (1673-1726), duke of Schleswig-HolsteinGottorp, bishop of Lubeck, and administrator, during the war of 1700-1721, of the duchies of Holstein-Gottorp for his nephew Charles Frederick; his mother was Albertina Frederica of BadenDurlach.
It was erected under the will of his daughter Frederica, a resident of Ealing.
His unfortunate first marriage with his cousin Charlotte Frederica of MecklenburgSchwerin was dissolved in 1810.
On the 21st of August 1745, by the command of his aunt, he married the princess Sophia Augusta Frederica of AnhaltZerbst, who exchanged her name for that of Catherine Aleksyeevna.