Frederick William I, Duke of Schleswig-Holstein-Sonderburg-Beck

Frederick William I, Duke of Schleswig-Holstein-Sonderburg-Beck (German: Friedrich Wilhelm I. Herzog von Schleswig-Holstein-Sonderburg-Beck; 2 May 1682 – 26 June 1719) was a son of Duke August and his wife, Countess Hedwig Louise of Lippe-Alverdissen (1650-1731).

Since he had no surviving male heir, he was succeeded as Duke of Schleswig-Holstein-Sonderburg-Beck by his paternal uncle Frederick Louis.

In Munich, Bavaria, on 8 February 1708, he married Maria Antonia called Antoinette Josefa Isnardi di Castello, 8th Countess of Sanfré (Munich, Bavaria, 15 October 1692 – Vienna, Austria, 17/18 February 1762), sister of Ignazio Giambattista Isnardi di Castello, 6th Marquess of Caraglio and 7th Count of Sanfrè, Marquess of Lenoncourt and Marquess of Balinville, and daughter of Francesco Antonio Massimiliano Emmanuele Isnardi di Castello (14 July 1658 – ?

They had two surviving daughters: After his death in 1719, his widow, the Duchess Antoinette Josefa (1692-1762) inherited Haus Beck, near Ulenburg, then in Minden-Ravensberg, Brandenburg, Brandenburg-Prussia.

But, in 1732, she sold it to the actual Duke, her late husband's first cousin Frederick William II.