Margravine of Bayreuth . Name variations: Friederike Sophie Wilhelmine. Born Frederica Sophia Wilhelmina in 1709; died in 1758; daughter of Sophia Dorothea of Brunswick-Lüneburg-Hanover (1687–1757) and Frederick William I (1688–1740), king of Prussia (r. 1713–1740); sister of Frederick II the Great (1712–1786), king of Prussia; married Frederick, margrave of Bayreuth.
Throughout both his childhood and adult life, Frederick II the Great maintained his closest relationship with his sister Wilhelmina. Corresponding regularly, they discussed literature, philosophy, affairs of state, and anything else of a public or private nature. It was she who provided solace during the darkest days of his relationship with their father.