Wilhelmine, Gräfin von Lichtenau, born as Wilhelmine Enke, also spelled Encke (29 December 1753 in Potsdam – 9 June 1820 in Berlin), was the official mistress of King Frederick William II of Prussia from 1769 until 1797 and was elevated by him into the nobility. She is regarded as politically active and influential in the policy of Prussia during his reign.
Her father, Johann Elias Enke, was a chamber musician in service of King Frederick II of Prussia. Wilhelmine met Crown Prince Fredrick William in 1764. The king preferred that the crown prince maintain a relationship with her rather than have changing relationships with foreign women, and in 1769 she became the crown prince's official mistress. The couple had five children, of whom only one survived to adulthood:
- A daughter (born and died 10 August 1770).
- Ulrike Sophie von Berckholz (March 1774 - 5 September 1774).
- Christina Sophie Frederica von Lützenberg (25-31 August 1777).
- Count Alexander von der Marck (4 January 1779 - 1 August 1787), reportedly the King's favorite child; he was probably poisoned.
- Countess Marianne Diderica Frederica Wilhelmine von der Marck (29 February 1780 - 11 June 1814), married firstly on 17 March 1797 to Hereditary Count Frederick of Stolberg-Stolberg (they divorced in 1799), secondly on 14 March 1801 to Baron Kaspar von Miaskowksi (also divorced) and thirdly in 1807 to Etienne de Thierry. She had four daughters in her three marriages, the eldest of them was the notorious poet Countess Louise of Stolberg-Stolberg.
In 1782, Fredrick William arranged for her to marry his councillor and chamberlain Johann Friedrich Rietz (1755–1809), but the relationship between Wilhelmine and Fredrick William continued.
It is debated whether Wilhelmine co-operated with Johann Rudolph von Bischoffswerder and Johann Christoph von Wöllner to keep the monarch under control. Wilhelmine was given the title Countess von Lichtenau in 1794, but that was not made public until 1796.
After Frederick William died in 1797, Wilhelmine was exiled and her property confiscated, although she was granted a pension (1800). In 1802 to 1806, she was married to the dramatic Franz Ignaz Holbein, known as "Fontano" and 26 years her junior, in Breslau (now in Poland and renamed Wrocław). In 1811, Napoleon allowed her to return to Berlin.
Wilhelmine, known popularly as "Beautiful Wilhelmine", is closely associated with the Marmorpalais in Potsdam. As Friedrich Wilhelm II's official mistress, she had great influence on the interior decoration of the palace. Following plans by Michael Philipp Boumann, an early classicist style townhouse called Lichtenau Palace was erected for her at the edge of Potsdam's Neuer Garten, at a site on today's Behlertstrasse.
During her lifetime, she was the subject of satire, and following fake memoirs, she published her own. She is a main character in Ernst von Salomon's 1965 novel Die schöne Wilhelmine, which also was turned into a 1984 television serial.