King Charles was at an environment reception for London climate action week on Wednesday - on what was the hottest June day on record.
An aide fanned the King during the reception as temperatures soared to 35.8C in the UK.
Energy Secretary Ed Miliband spoke at the event - telling guests at St James's Palace that a nurse was on hand if anyone was affected by the heat.
Mr Miliband said: "The very fact that we have to do that here in the UK in June says quite a lot about the circumstances that we are in."
Other speakers at the event - aimed at accelerating momentum on super-pollutant action - included UN Secretary-General Antonio Guterres and Mia Mottley, the prime minister of Barbados.
Mr Miliband added: "First, as I said at the outset, here we are in London on a 35C day.
"This didn't used to be normal, but unfortunately it is now the new normal, and we know that reducing methane emissions and other super-pollutants is one of the best things we can do to act on the climate crisis.
"We know we have to, because we know this is at best the new normal and at worst the coolest summers we're going to have in the future, and that is a very chastening thought."
It was a busy day for the King, who also visited one of the world's leading Brazilian Jiu Jitsu schools in the country - the Roger Gracie Brazilian Jiu Jitsu Academy in Hammersmith - where he chatted with rapper Tinie Tempah.
The artist, who rose to fame with his song Pass Out, took up the sport after being introduced to it by actor Tom Hardy.
On the King's interest in Brazilian Jiu Jitsu, the rapper said: "He was basically saying that he's been wanting to champion this in some capacity for ages, and that he has been talking to Idris (Elba) about it, and maybe I could be of service in some capacity.
"Because he wants to use it to help young people, and I said to him that that is basically my ambition."
Charles also met the women's cricket team of Afghanistan at Clarence House.
The team are asking to be recognised by the International Cricket Council (ICC) so that they can compete internationally.
Wicketkeeper Ekil Latifi, 21, who fled Afghanistan in 2021, said: "We want the ICC to allow us to play under the [Afghanistan] flag and name.
"Whatever the men do, we want to do the same thing for our country.
"We're not just representing ourselves and the team, but also Afghan women back in our country. We're representing them and all the things they can't do there.
"We want to show that women aren't afraid to do anything they want to."
(c) Sky News 2026: Charles joins climate reception on hottest June day on record
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