Army of the Holy Roman Empire
In 1725, the king invested the duke with the Riesenberg estate, however, he sold it off. In 1732, he purchased Beck Manor in Löhne-Ulenburg, after which the Schleswig-Holstein-Sonderburg-Beck line was named, from Maria Antonia, the widow of his cousin Frederick William I (1682–1719), who had converted to Catholicism and had become a field marshal in the Army of the Holy Roman Empire. Frederick William I fell in battle at Francavilla di Sicilia.