The King will not attend the Cop29 climate summit being hosted by Azerbaijan next month, it is understood.
Charles has long campaigned on environmental issues but will be absent from the United Nations gathering being held in the oil-rich state from November 11 to 22.
The head of state has been receiving treatment for an undisclosed form of cancer since early in the year and the global climate change conference will begin just over two weeks after the King and Queen Camilla’s long-haul trip to Australia and Samoa ends.
The overseas tour has been curtailed on doctor’s advice, with a visit to New Zealand dropped from the itinerary and other changes to the programme.
At the time the visit was announced a Buckingham Palace spokesman said: “We’ve had to make some difficult decisions about the programme with the Australian government, about where their majesties can get to.”
The King will also pause his cancer treatment during the 11 days he is away from the UK.
Charles missed Cop27 in 2022, the first climate change summit of his reign, after a “unanimous agreement” was reached that the King should not attend the gathering in Egypt after advice was sought by his office from Liz Truss’s government.
But the following year the head of state delivered an address on the opening day of Cop28 in Dubai, warning delegates that the world remains “dreadfully far off track” in key climate targets and called for meaningful change.
