The King was told by Liz Truss not to attend the COP27 climate summit in Egypt, Downing Street confirmed on Friday.
No10 said the advice had not changed under new Prime Minister Rishi Sunak.
King Charles, a passionate environmentalist, asked advice about whether he could attend the global conference being held in Sharm El-Sheikh from November 6 to 18.
The Prime Minister's spokesman said: “As is standard practice, Government advice was sought and provided under a previous PM and it was unanimously agreed that this would not be the right occasion for the King to visit in person.
“I’m not aware that advice has changed.”
The annual UN climate meetings are designed to help governments agree steps to limit world temperature rises.
The UK hosted last year’s COP26 in Glasgow, with then-PM Boris Johnson stressing the need to act by warning it was a “one minute to midnight moment”.
Environment Secretary Thérèse Coffey said she and “several senior government ministers” will be attending.