The unauthorised book by Richard Barber, a magazine journalist, has already been strongly criticised by a close family member and sets out a picture of a damaged and overly assured man who is often reckless in his handling of other people's feelings.
Among the revelations contained in the biography - called Earl Spencer: Saint or Sinner? and published by Andre Deutsch - is the claim that at one point during his time as a broadcast journalist in the late 1980s and early 1990s Charles was on the brink of presenting a television version of the weekly magazine Hello! This career move, suggests Barber, is hardly consistent with the earl's subsequent stand on press intrusion and the sanctity of the private lives of the aristocracy.
In an interview with the magazine's publishing director, Sally Cartwright, Barber is told that the involvement of Diana's brother in the project was the clinching factor in the TV deal. Plans for the programme were apparently only scuppered by the sudden death of Charles's father and Charles's subsequent inheritance of the Althorp title.
A spokesman for Earl Spencer confirmed yesterday that Charles could indeed remember some question of a Hello!-style show, but had never seriously considered the job.
Aside from teachers and anonymous school friends, Barber interviews one of the Spencer family nannies who was most closely associated with Charles's early childhood. Mary Clarke speaks fondly of her charge, but does shed some doubt on the idea that he and his big sister Diana were ever particularly close. She remembers Charles as a quiet boy who would sit back and allow his sister to "sparkle" when she returned on holidays from boarding school. "Nor can I honestly say that there was an exaggerated bond between them," she tells the author.
Barber's book chronicles Charles's successful career at Eton and Oxford, listing a series of girlfriends and detailing at length one well-known adulterous relationship in a chapter entitled "The Sally Ann Lasson Affair". This concentration on his personal relationships has upset close family members.
Commenting on the book this week, a near relative of the late earl, Charles's father, said: "The author seems to know nothing about Charles at all. I don't agree with these unauthorised biographies. A lot of what has been written is completely untrue nonsense."
In each era of the earl's life Barber's biography emphasises a penchant for melodramatic and, arguably, tasteless shock tactics: in fact exactly the kind of behaviour that might have led friends and family to expect something provocative from his funeral address in Westminster Abbey.
Among the principal interviewees Barber spoke to in compiling information for the book is the earl's faithful public relations assistant Shelley Ann Claircourt. She says she now regrets her co-operation with the author, but explains the error of judgement by saying she was concerned Barber should not be left to repeat inaccurate tabloid newspaper stories.
"I spoke mainly about the divorce to Mr Barber because I was worried that if he was relying on cuttings there would be a problem," she said.
"The earl didn't help with the book in any way and he told his friends that they should make their own minds up whether or not they wanted to contribute."
Aside from her loyal comments on the pain of the earl's recent divorce from Victoria Lockwood, Ms Claircourt insists that the earl was the original and only author of his devastating funeral speech.
This first biography presents the earl as a man who is very jealous of his reputation, who wants to be treated normally and yet who celebrated his 21st birthday with an epic party that featured a live satellite link to Los Angeles.
He was the Spencer's longed-for son and heir, brought up to see himself as the centre and future of the family, but then suddenly pipped at the post by Diana's global fame.