He was only the
titular duke, because he did not inherit the
domain of Beck. It had been inherited by Duke
Frederick William I, the son of his elder brother, Duke
August, in 1689. Duke Frederick William I was killed in the
Battle of Francavilla in
Sicily in 1719, leaving a widow,
née Maria Antonia called Antoinette Josepha Isnardi di Castello, Contessa di Sanfré (1692–1762), and two
minor daughters. In 1675 he participated in the
Battle of Fehrbellin as a
Rittmeister. The following year he was a colonel in the Holstein dragoons. Frederick Louis was named lieutenant general and Governor of
Wesel in 1690. Three years later he was appointed commanding general of the
Duchy of Prussia. On 17 January 1701 Frederick Louis received the
Order of the Black Eagle from the new King
Frederick I of Prussia and shortly afterward was named
Statthalter of the
Kingdom of Prussia and Governor of
Königsberg. During the
War of the Spanish Succession, he participated in the
Battle of Oudenarde in 1708, the
Battle of Malplaquet in 1709, and the sieges of
Lille,
Mons, and
Tournai. Frederick Louis was promoted to field marshal in 1713. The duke also secured neutrality for Prussia during much of the
Great Northern War. He died in Königsberg and was buried alongside his wife in
Königsberg Cathedral. == Marriage and issue ==