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

Frederick William I, Duke of Duke of Schleswig-Holstein-Sonderburg-Beck (German: Friedrich Wilhelm I. von Schleswig-Holstein-Sonderburg-Beck; 2 May 1682 – 16 June 1719) was a son of Duke August and his wife, Philippa Louisa of Lippe-Buckburg.He succeeded his father as Duke of Beck in 1689.

He converted to Roman Catholicism and joined the Army of the Holy Roman Empire.He died of his wounds in the Battle of Francavilla in Sicily in 1719.

Since he had no male heir, he was succeeded as Duke of Beck by his uncle Frederick Louis.

In 1708, he married Marie Antoinette (15.10.1692-1762), the daughter of Francis Anthony Maximilian Emmanuel Isnardi di Castello, 5th Marquess of Caraglio and 6th Count of Sanfré, in Piedmont, and wife Maria Magdalene Grundemann von Falkenberg, heiress of Sanfré and Strevi. They had two daughters:

• Maria Ana Leopoldina (b. Linz, Vienna, 2.8.1717 - Torino, 7.2.1789). She was married in Vienna on 4.8.1735 to D. Manoel de Souza (21.7.1703 - in a fire, in prison, in Lisbon, 1759), Lord of Calhariz, in Portugal. Their son, D. Alexandre de Sousa Holstein (Lisbon 4.12.1751 - 13.12.1803) was Lord of Calhariz, count of Sanfré, Portuguese ambassador do the courts of Kopenhagen, Berlin and Rome.
• Johanna Amalia (b. 1719- d. 1774) Married in 1740 Emanuel Silva Tarouca