The Queen will meet senior royals in Sandringham later to discuss the future roles of the Duke and Duchess of Sussex.
Prince Harry, the Duke of Cambridge and the Prince of Wales will all attend, while Meghan is expected to join the discussion by phone from Canada.
The Sussexes say they plan to step back as senior members of the Royal Family.
BBC royal correspondent Jonny Dymond described the meeting as "royal history in the making".
It is hoped the talks will produce a "next step" on the way to defining the couple's new relationship with the Royal Family - in line with the Queen's wish to find a solution within days.