The Commonwealth has secretly begun considering who might succeed the Queen as its head, the BBC has learned.
The issue is hugely sensitive because the role is not hereditary and will not pass automatically to the Prince of Wales on the Queen's death.
The Commonwealth has set up a "high level group" to look at the way the international organisation is governed.
This group is meeting later, officially to review how the Commonwealth is run by its secretariat and governors.
However, senior sources added that the gathering in London would also consider what happens when the Queen, who turns 92 in April, dies.
The group is expected to report to the Commonwealth Heads of Government Meeting (CHOGM) in London in April, which is likely to be the last that the 91-year-old monarch will attend.
A second source said the issue of the succession is expected to be discussed by Commonwealth leaders on the margins of the summit, particularly when they meet without officials "on retreat" at Windsor Castle.
The Queen was proclaimed Head of the Commonwealth at her coronation when she was head of state in seven of its eight members.
It is not an hereditary position that will pass automatically to her son, who will be head of state in only 15 of the 53 member nations that now make up the Commonwealth.
Any decision about the future would have to be made by the Commonwealth heads of government at the time of the Queen's death. But there is no formal process for choosing her successor.
The Queen has been working in private to try to ensure that Prince Charles does succeed her, sending senior officials around the world to lobby Commonwealth leaders, reports BBC.