Queen Elizabeth II will miss the Commonwealth heads of government meeting in Sri Lanka in November, sending her heir Prince Charles in her place, the palace announced on Tuesday.
It will be the first time the 87-year-old monarch has missed such a meeting since it was first held in 1971, and comes as she hands over some of her duties to younger members of the royal family.
The queen was forced to cancel several public engagements earlier this year after being admitted to hospital suffering from gastroenteritis, her first hospital admission in 10 years.
"The queen will be represented at this year's Commonwealth heads of government meeting (CHOGM) by the Prince of Wales," Buckingham Palace said in a short statement.
A palace source said the decision was unrelated to the controversy over Sri Lanka's human rights record, which has prompted Canada to threaten to boycott the meeting.
There had been a question mark over British Prime Minister David Cameron's attendance, but his office said he would be making the trip, while delivering a "very tough message" that Colombo must make progress on human rights.
The queen attended the last Commonwealth meeting in Australia in 2011 in her role as the symbolic head of the 54-member organisation, which is made up primarily of former British colonies.
Her decision to stay away this year follows a gradual move to cut down her long-haul foreign trips, which last year saw some of the younger royals represent the elderly monarch on overseas tours to mark her Diamond Jubilee.
Hosts Sri Lanka said that Prince Charles, who as heir to the throne will take over his mother's Commonwealth role when she dies, would be warmly welcomed to the November 15-17 meeting.
"Whilst paying enormous tribute to Her Majesty's continuing dedication and deep sense of duty to the Commonwealth, Sri Lanka warmly welcomes... the Prince of Wales, to Colombo, Sri Lanka, for CHOGM 2013," the government said in a statement.
Prince Charles accompanied his mother to the heads of government meetings in Edinburgh in 1997 and Kampala in 2007, and also stood in for the queen at the Commonwealth Games in New Delhi in 2010.
Deputy Prime Minister Nick Clegg said the decision not to send the queen to Sri Lanka had likely been taken "very, very carefully, because I know the queen cares enormously for the Commonwealth".
"We should respect that decision particularly because the queen has been so tireless in her service to the Commonwealth," he told Sky News television.
The Sri Lanka meeting has been mired in controversy, with Canada threatening to stay away unless Colombo investigates suspected war crimes committed by its troops in 2009.
Prime Minister Cameron will attend but will press President Mahinda Rajapakse's regime on allegations of rights abuses.
"He feels that the Commonwealth is a hugely important group and that the work it does is very important," a spokesman for the prime minister's Downing Street office said.
"Furthermore, he can go there and take a very tough message to the Sri Lankan government that they need to make concrete progress on human rights, reconciliation and political settlement."
Rajapakse's regime faces allegations -- which it denies -- of indiscriminately killing civilians during the final assault on Tamil Tiger rebels that ended a four-decade civil war.