Hollywood legend Russell Crowe says 'we don't need a King' - and has recalled how he sent Palace officials into a spin by addressing Princes William and Harry as 'mate'.
Although the Gladiator star says he has respect for the institution, he refuses to say 'Your Highness' when in royal company.
It has been reported that Coronation celebrations are estimated to be costing up to £100 million and the film star feels the money could serve a greater purpose.
The 59-year-old says that, although the sovereign is a "good bloke", he believes the Firm are outdated and should be scrapped.
In a lengthy series of tweets, the actor recalled meeting the then Prince with his former wife, the late Princess Diana at a royal film premiere in 2003.
The New Zealand-born star said: "Dani was six months pregnant with our first. We did the obligatory conga line of cast introductions, then we sat with him for the film.
"The man who would be King was kind. He was also funny. Deeply intelligent and good company, and gallant in his deference to Dani’s pregnancy. I’ll never forget the warmth in our last hand shake. Good bloke."
But the New Zealand actor explained that his respect for the Royals only went so far, as he detailed his disdain of greeting them by their official titles.
"In any of my meetings with royalty, I haven’t yet been able to utter the ‘your highness’," he went on.
"It simply doesn’t come out of my mouth. It’s not in my DNA. I called both William and Harry ‘mate’ when I met them. I thought the equerry (an officer of the British royal household) was going to pass out.
"That doesn’t mean however that I meant any disrespect or discourtesy. Far from it. I was pleased to meet them.
"I view the costumes and the ritual and the pageantry with distant interest, if any. I don’t know what it’s all supposed to mean in 2023, nor in any other time for that matter. I don’t really think we need a King, but I’m sure Charles III will do the very best job he can."
He added: "I don’t think any of us can really understand what that life of duty and expectation must feel like.
"He’s taking over the family business. That is his destiny. Like it is for many, from publishers to plasterers."
He told his followers "don't bother sending abuse" and received a mixed response to his tweets.
One said: "Since 1976 King Charles III has helped 1 million young vulnerable ppl between ages 11-30 yrs old using his merge retirement money from Navy days with Princes Trust. Royal family have done huge amounts for charity through their royal brand and for our economy."
But another put: "In the UK, people are struggling to heat their homes and feed themselves. Healthcare, education etc. are severely under funded.
"Yes, this is due to the Tories, but the Royal family can do so much for the people but they turn their noses at us with their fingers in their ears."