The macabre message was on Friday being used by protesters rioting against President Macron’s decision to raise the retirement age from 62 to 64.
There have been nightly riots, and they were set to intensify if – as planned – the King had arrived in Paris on Sunday.
“I think it would not be responsible and would lack some common sense if we invited His Majesty the King and the Queen Consort for a state visit in the midst of the demonstrations,” Mr Macron said on Friday.
“So, out of friendship, respect and esteem for His Majesty the King and Queen Consort, and for the British people, I took the initiative this morning to call and tell him what the situation was.”
Senior politicians including Mr Macron had received threats evoking the guillotine used to execute Louis XVI and Marie Antoinette – the last rightful King and Queen of France.
The words “Death to the King” had even appeared in bright red graffiti on Place de la Concorde – the central Paris square where Louis and his wife were killed.
Another scrawled message read “Charles III do you know the guillotine?”
The French feared the security of King Charles could not be guaranteed “because of his interest in mingling with crowds,” according to security sources.
A crack team of officers from the SDLP Protection Service unit rigorously studied the monarch’s profile.
“They became aware of the King’s habit of impromptu handshakes, and talking to ordinary people whenever he could,” said a source who was involved in the planning of four-days of events.
“There are huge social tensions in France, and there is no doubt that such good manners could have been very dangerous indeed.”
The development was a major humiliation for Mr Macron, especially as a visit to Germany by the Royal couple next week will go ahead as planned.
Eric Ciotti, leader of the opposition Republicans party in France, said the chaotic security situation was a national embarrassment.
“The visit of Charles III is cancelled by the government due to social unrest,” said Mr Ciotti.
“What an image for our country, which is not even able to ensure the security of a head of state”.
Referring to Mr Macron as a “republican monarch”, Left-Wing firebrand MP and former presidential candidate Jean-Luc Mélenchon said he was “delighted to see the meeting of kings at Versailles broken up by popular censorship”.
Raquel Garrido, another member of the hard Left’s Nupes parliamentary coalition, said she hoped Mr Macron would now resign, saying: “Two kings were set to meet at Versailles – one down, one to go.”
And Manuel Bompard, of the Party of the Left, said: “This shows the fragility of Emmanuel Macron as head of state.
“Charles III has backed down, now we hope Macron will back down too.”
Others pointed to how Mr Macron had been prepared to meet a foreign king, but not trade unionists battling to reverse his pension reform.
Nupes MP Alexis Corbière said: “Since he’s no longer hosting the King of England , Charles III, perhaps Macron can host the trade unions?”
Green Party MP Sandrine Rousseau, who had called for the cancellation of the state visit, said: “It’s good that it’s been postponed, it was madness to make this visit in the middle of a social conflict of historic proportions.
“To go and eat at Versailles, to drive down te Champs-Élysées – nothing was going to go well. The protesters were not going to roll out the red carpet for the king.”
Mr Macron said he would attend Charles’s Coronation in London in May, and suggested the new date for the King’s visit to France would be in the ‘early summer’.
Buckingham Palace said in a statement: “The King and the Queen Consort’s state visit to France has been postponed.
“Their majesties greatly look forward to the opportunity to visit France as soon as dates can be found.”