Britain s King Charles III, flanked by Britain s Camilla, Queen Consort, speaks during the presentation of Addresses by both Houses of Parliament in Westminster Hall, inside the Palace of Westminster, central London, following the death of Queen Elizabeth II on September 8. AFP
Instead, he plans to protest on the historic royal occasion, dressed in a yellow T-shirt with the provocative slogan: "Abolish the monarchy."
"The monarchy has no place in modern society given how outdated and undemocratic it is," King, 40, told AFP.
He aims to join other protesters rallied by the pressure group Republic, which wants the monarch replaced by an elected head of state.
Republicans have long been a fringe group in Britain. But their voices have been getting louder since the death of Queen Elizabeth II last year.
Charles, who inherited the crown automatically, has been trailed by protesters holding up signs proclaiming: "Not my king!"
Republic's chief executive Graham Smith sees the spectacle of dazzling jewels and golden carriages as a chance to make their case, particularly as Britons struggle with the rising cost of living.
That makes it "more fertile ground" for recruitment. "People are far more willing to listen and engage," he added.
Times have also changed since Britons gave deference to those deemed their social superiors.
"People are far more critical generally of our political system, which comes into this whole debate not just about the royals but about the constitution and the government and parliament," Smith said.
"And they are far less interested in the royals."
Royal commentator Richard Fitzwilliams agreed that for the first time, the republican movement was "showing its teeth".
But he said it still failed to have major political support.
To get its point across, Republic has become more active than ever on social media, to try to mobilise its 130,000-strong base and expand its numbers.
It sends out regular emails about upcoming protests, including last week for a visit by the king and queen to Liverpool, in northwest England.
"Not my king" placards have as a result become more visible. Such protests were virtually unthinkable during Elizabeth's reign.
A recent YouGov poll indicated that most Britons (58 percent) still support the monarchy. But Smith still sees that as at most "tepid".
"You're still going to get a good crowd in London (on coronation day)," he added.
"A lot of people will go because they want to see something which is historic... it doesn't necessarily translate into royalism."
Republicans prefer instead to concentrate on levels of support among younger people.
The YouGov poll indicated that 32 percent of those aged 18-24 supported the monarchy, against 38 percent who wanted an elected head of state.
"Polling that shows attitudes towards the monarchy are changing as the younger generation comes to the fore and quite rightly asks themselves, what's the point of the monarchy?" said King.
But Sean Lang, a history professor at Anglia Ruskin University, disagrees: young people have never been enthusiastic about the monarchy, he said.
"I think republicans who see the polling as evidence that the end of the monarchy is round the corner are indulging in wishful thinking," he added.
Unlike the revolutionaries of old, who brought down foreign kings and queen with violence, Smith does not see the current crop of republicans as radicals.
"What we're proposing isn't particularly radical, it's democratic," he argued.
Instead of the hereditary principle of monarchy, they want a fully elected parliament and elected head of state, plus a written constitution that clearly separates powers.
"Our focus is getting the public on board and to push for a referendum," he said.
Unlike recent direct action protests in London by environmental groups, Smith says they have "no plans to disrupt the actual procession".
They are expecting supporters to be spread out along the route with about 1,000 at Trafalgar Square to chant "Not my king" as Charles passes by.
"There are huge swathes of society in desperate need of help and those are all far worthier causes for where our money should be spent," said King.
"Parading a gold carriage through the capital isn't going to solve any of these problems."