Charles was "disappointed" after Trump called him the "Prince of Whales," spelled like the sea mammal, rather than the correct way: Prince of Wales, author Christopher Andersen writes The King: The Life of Charles III.
Charles was also turned off when Trump said Princess Diana could have been his lady.
"It didn't help that Trump had aggressively pursued Princess Diana after her divorce — overtures that were rebuffed — and claimed later on a radio program that he could have 'nailed her if I wanted to,' but only if she passed an HIV test," Andersen writes.
Trump also commented on Kate Middleton's topless sunbathing photos, which were published in a magazine in 2012, saying, "Kate Middleton is great – but she shouldn't be sunbathing in the nude – only herself to blame. Who wouldn't take Kate's picture and make lots of money if she does the nude sunbathing thing. Come on Kate!"
Trump's words did not sit well with Charles and Prince William. "Trump's criticism of Kate resulted in what one Clarence House butler referred to as 'torrents of profanity' from both Prince Charles and his sons," Andersen writes.
When Trump tried to visit Britain in 2017, the royals were adamantly against it. Charles, William and Harry "burned up the phone lines between Clarence House and Kensington Palace, with all three princes agreeing to work behind the scenes to discourage Trump's visit," according to Andersen.
"Throughout 2017 and into 2018, Britons seemed nearly as fascinated with the tweet-storming Trump as their American cousins. The royal family was no exception," Andersen wrote. "At every opportunity, including Prince Harry's wedding reception, Charles took his wealthy and influential American friends aside and gently prodded them for information.
"It was important that he not push too hard or too far; some of the donors to his charities, including those with the deepest pockets, were Trump supporters," he continued.
"Still, when lent a receptive ear, Charles asked on several occasions how likely it was that President Trump would be impeached. 'Trump seems to be detached from reality, doesn't he?' he asked a former Washington official who now headed up a major US conglomerate. 'What a ghastly, awful man.'"
Of course, in 2018, Trump shared why he didn't head over to the U.K.
"Reason I canceled my trip to London is that I am not a big fan of the Obama Administration having sold perhaps the best located and finest embassy in London for 'peanuts,' only to build a new one in an off location for 1.2 billion dollars. Bad deal. Wanted me to cut ribbon-NO!" he wrote at the time.
For more on the royal family, tune into the new podcast "The Firm: Blood, Lies and Royal Succession." Listen below!