To be privately owned
Bredebeck Castle

Built at the beginning of the 20th century, Bredebeck Castle, a stately manor house, is located in Lower Saxony. It is now privately owned.
History+
The current Bredebeck Castle was built in 1901 and 1902 by order of the farmer Hellberg. Originally designed as a manor house, it was sold in 1909 for 160,000 Reichsmark to Major a. D. von Rosen, who resold it in 1922 to the lawyer Adolf Kühling. Kühling had the building, which at that time consisted only of the central section, extended with side annexes. In 1932, ownership passed to Ernst Kühling. In 1936, the castle grounds were integrated into the Bergen military training area. Since 1945, it has served as an officers' mess for the British regiments stationed there and occasionally as a guesthouse, which has also been used by the British royal family.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Schloss_Bredebeck.jpg
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 52.7873, 9.8902