Biographer Simon Heffer said he believes Prince Harry’s decision to cross his father’s reported ‘red line’ by disparaging Camilla could leave King Charles’ sympathies for his son “irrevocably strained” and make Harry the “only long-term casualty” from his own revelations.

He wrote: “The Duke seems oblivious to the fact that his stepmother now occupies a higher place in the public’s regard than he does – thanks not just to her own public service, but also to his own ill-judged behaviour.

“He cannot see that most of his father’s subjects will regard his disloyalty towards his family – even to his stepmother – as an act of delinquency, and as unforgivable. Despite the Queen’s absence from what he describes as the troubled early years of his life, she now finds herself dragged into her stepson’s orgy of exhibitionism.”

In Prince tell-all memoir Spare, set to be released officially in the UK tomorrow, he makes a series of accusations he has doubled-down on or expanded on in a series of interviews both in the UK and in the US.

He told ABC’s Good Morning America the Queen Consort had “sacrificed me on her personal PR altar” and attacked what he alleged was Camilla’s attempts to “rehabilitate” her image, after being cast as the “third person” in his parents’ marriage.

Separately, he sympathised with her, saying in the interview with ABC’s Good Morning America (GMA) she was not an “evil stepmother”.

GMA co-host Michael Strahan read an extract from Harry’s book critical of the Queen Consort which said: “In a funny way I even wanted Camilla to be happy. Maybe she’d be less dangerous if she was happy.”

Another excerpt said: “I have complex feelings about gaining a step parent who I thought had recently sacrificed me on her personal PR altar.”

Asked what Camilla had “done” at that point, Harry replied: “I have a huge amount of compassion for her, you know. Being the third person within my parents’ marriage and she had a reputation, or an image, to rehabilitate.

“Whatever conversations happened, whatever deals or trading was made right at the beginning, she was led to believe that that would be the best way of doing it.”

In a separate interview with CNN’s Anderson Cooper, Harry said Camilla’s willingness to forge relationships with the British press made her “dangerous” and there would be “bodies left in the street because of that”.

Mr Heffer says that Camilla has already endured her fair share of public scrutiny since her relationship with the then Prince Charles was revealed. He said the Royal Family’s stategy of “never apologise, never explain” was something that will again serve them well in the crisis with Prince Harry.

Mr Heffer said the Duke’s “embarrassing emotional incontinence” was juxtaposed to the “dsicreet” and “civilised” way the Royal Family were behaving that allowed them to earn the British public’s “respect and support”.

Describing Prince Harry using weapons such as “self-pity” and “disloyalty”, Mr Heffer said only person who these weapons may “prove lethal” to would be the Duke of Sussex himself.