Prince Harry and Meghan are said to be planning to relocate from the U.S. later this month to a private residence outside London.
The reunion at Highgrove House is the family's first known meeting since 2022.
Prince Harry's final lawsuit aimed at taming the British tabloids ended in defeat as a judge found he failed to prove his privacy invasion claims against the publisher of the Daily Mail.
Harry is visiting London solo after deciding against bringing his wife Meghan and their two children.
Catherine, Princess of Wales, completed Britain's arduous Three Peaks Challenge over the weekend to support the hospital where she underwent cancer treatment two years ago.