Frederick William III, Duke of Schleswig Holstein Sonderburg Beck

Frederick William III, Duke of Schleswig-Holstein-Sonderburg-Beck (4 November 1723 – 6 May 1757) was a son of Frederick William II and his wife, Ursula Anna of Dohna. He succeeded his father as Duke of Beck in 1749.

Frederick William was a recipient of the Order of the Red Eagle. He served as a colonel in the Prussian Army and was commander of the Füsilier Regiments No. 46 (Old-Württemberg). During the Seven Years' War, he fell in the Battle of Prague in 1757. He was unmarried and childless; he was succeed as Duke of Beck by his uncle Charles Louis.