Boris Johnson's supposed animosity towards Prince Charles first surfaced when he struggled to come up with a fitting tribute to the future king in a eulogy, it has been claimed.
The Prime Minister was asked by the BBC to film an interview in the event of the sudden death of the the heir to the throne two years ago.
He was also requested to say some words about the Princess Royal by the broadcaster.
But while Mr Johnson was said to be enthusiastic about Princess Anne, he struggled to find anything positive to say about the Prince of Wales, it is claimed.
It comes after Charles reportedly branded the Government's plans to send migrants to Rwanda "appalling".
The Times reports Charles is understood to be particularly frustrated at Mr Johnson’s asylum policy as he is getting set to represent his mother the Queen at the Commonwealth Heads of Government meeting later this month.
Ahead of the BBC commitment, the PM reportedly told aides before the interview that he "did not like" Charles - and made a series of jokes instead of paying a personal tribute, sources say.
Toasting his Duchy Organic biscuits, he joked that Charles was the “king of biscuits” and said he feared that he would “take the recipe to his grave”.
The Times suggest courtiers feel Mr Johnson has shown “disrespectful” behaviour towards him.
His relationship with Charles is said to have turned after he arrived in a “shambolic state” on a visit to see the royal at his home in the Scottish Highlands.
Mr Johnson is said to have been “distracted” and “clearly not focused” during their meeting.
On the Rwanda row, the Prime Minister told LBC Radio: “I do think that it’s the job of government to stop people breaking the law and to support people who are doing the right thing. That’s what we are doing.”
A source reportedly heard Charles, 73, expressing his frustration at the policy, telling the newspaper: "He said he was more than disappointed at the policy.
"He said he thinks the Government’s whole approach is appalling. It was clear he was not impressed with the Government’s direction of travel."
Mr Johnson’s official spokesman said: “The Prime Minister has nothing but respect and admiration for the Prince of Wales, who’s spoken out on a number of issues, not least the environment.”
