The Queen will miss the Commonwealth Heads of Government meeting for the first time since 1973, Buckingham Palace has confirmed.
The Prince of Wales will represent the Queen, who is head of the Commonwealth, at the meeting in Sri Lanka in November.
A 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.
"As a result of that she won't be travelling to the Commonwealth Heads of Government Meeting (CHOGM) later this year."
The Queen, who is 87, was first present at CHOGM in Ottawa, Canada, in 1973 - missing the first one in 1971 - and has been at every summit since.