King Charles faced a shocking attack from the figure who had claimed to have known him "for a long time".
President Donald Trump shared a doctored video of Charles, suggesting that the monarch ignored a man who was fainting, raising concerns and questions.
What did the edited video show?
In the edited clip, an Asda worker collapses in front of the monarch, who puts his hand in his pocket and appears to walk away.
However, the full video, filmed in 2020, shows that Charles tried to stop the supermarket employee from falling, and only stepped away when it was clear he was receiving medical attention.The US president shared the clip on his Truth Social platform as part of a montage of world leaders seeming to ignore people in distress.
On the other hand, the video depicted Trump as "the people's president", greeting troops and police officers, honouring the war dead, hugging elderly veterans and being a doting husband.
The video came as a shock, as President Trump has often presented himself as a friend of King Charles.
The segment that included the King was filmed more than six years ago when he was the Prince of Wales. He is seen with the Duchess of Cornwall, visiting an Asda distribution centre in Bristol.
Trump and the British Royal Family
Trump is an enthusiastic supporter of the Royal family and the only US president to have made two state visits.
His fascination with the Royal family is believed to be rooted in his respect for Elizabeth II, whom he met twice, and whose coronation he watched on TV in 1953 with his mother, Mary Anne Trump, who was born in Scotland.
President Trump 'not a fan' of the Sussexes
Last week, the US president said he had had a "good relationship" with the King, who he "knew him as Prince Charles and King Charles" while criticising the Duke and Duchess of Sussex for being "terribly disrespectful" towards the Royal family.
He declared that he was "happy" that Prince Harry and Meghan Markle were moving back to Britain, noting, "I was not a fan."
During the King's US visit in April, he described the King as a "brave" and "fantastic" man.
Other figures portrayed in a negative way in the social media video were President Emmanuel Macron, Joe Biden and Barack Obama, both former Democratic presidents.