The Queen will not be attending this year's Commonwealth heads of government meeting for the first time since 1973, Buckingham Palace has said.
'Transition'
A Buckingham Palace spokesman said: "I can confirm that the Queen will be represented by the Prince of Wales.
"The reason is that we are reviewing the amount of long-haul travel that is taken by the Queen."
Our correspondent said the Queen would not have taken the decision lightly and it was both surprising and significant.
He said it was a significant moment for the Prince of Wales and it was also a symbolic move.
"It is about transition, about preparing this country for an elderly head of state who will be able to do less and less," he said.
"There is no intention of abdication. It will just not happen during her reign. It is the palace addressing the practicalities of her advancing age - you will see less of her and more of him."
By stepping in for the Queen, Prince Charles will be performing one of his most significant duties to date as a future King.
He has never before attended in place of the monarch at the two-yearly gathering of Commonwealth leaders. In 2007, both the Prince and the Queen attended CHOGM in Uganda.
The Queen was forced to cancel her appearance in March at the Commonwealth Day service at Westminster Abbey, the first time the monarch had missed the occasion in 20 years.
It was one of a number of engagements she cancelled after being admitted to hospital for gastroenteritis, which can cause vomiting, fever and stomach ache.
Politically tricky
The Queen sees the Commonwealth as a "family" and takes pride in its work.
The Queen, pictured here at the 2002 CHOGM in Australia, is passionate about the Commonwealth
Although she is its symbolic head, she has no formal powers over the 54 countries and two billion citizens which make up the voluntary association.
Concerns have been raised about the choice of Sri Lanka as the host nation for the 2013 summit.
Campaigners including Amnesty International are calling for the CHOGM meeting not to take place there before an investigation is carried out into human rights abuses in the final six months of the 26-year Sri Lankan civil war.
Britain is facing pressure to lead a boycott of the meeting, with Canada's government indicating it will not attend unless specific criteria are met.
But Buckingham Palace said the Queen's decision was not related to the political situation.
"The key point here is that the Queen will be represented, although she is not there in person, by the Prince of Wales," a spokesman said.
