To be privately owned
Frogmore Estate

The Frogmore Estate, a property on the grounds of Windsor Castle in England, is known for its royal burial sites, including the mausoleum of Queen Victoria and Prince Albert, as well as the private cemetery of the royal family.
History+
Frogmore House, the centerpiece of the estate, was built around 1680. In 1792, King George III acquired the house for Queen Charlotte. Later, it served as a residence for Queen Victoria's mother, the Duchess of Kent, who was interred in a mausoleum specially built for her in the park after her death. Around 1900, members of the royal family, including Admiral Prince Louis Alexander of Battenberg, resided here.
Source: Wikipedia · Licence: CC BY-SA 4.0
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: 51.4742, -0.5944