Spare is the story of a troubled young prince estranged from his family, ghostwritten by an author known for his expertise in fraught father-son relationships.

But the Duke of Sussex’s memoir is expected to let the King off lightly — and focus more on his frosty relationship with the Prince of Wales.

Following the Guardian’s reporting that Spare details a time Prince William attacked Prince Harry, a source with knowledge of the book, which will be published on January 10, told The Sunday Times they did not see how the brothers’ relationship could ever recover.

“Generally, I think the book [will be] worse for them than the royal family is expecting,” they said. “Everything is laid bare. Charles comes out of it better than I had expected, but it’s tough on William, in particular, and even Kate gets a bit of a broadside. There are these minute details, and a description of the fight between the brothers. I personally can’t see how Harry and William will be able to reconcile after this.”

In the Harry & Meghan Netflix documentary last month, Prince Harry claimed his brother “screamed and shouted” at him during the crisis talks in January 2020 about the Sussexes leaving the UK.

The source added that the book explores in depth Harry’s grief about his mother’s death: “The overall impression is that this is a man who has never recovered from the trauma of his mother dying so young, and then along comes Meghan and he projects onto her a parallel with Diana.”

“I personally can’t see how Harry and William will be able to reconcile after this.”

It is written by JR Moehringer, a Pulitzer prizewinning former journalist who also ghosted Andre Agassi’s best-selling autobiography.

Harry, who will read the audiobook himself, has donated some of the proceeds from Spare to charities including Sentebale, an organization he co-founded in memory of his mother to help children and young people in Lesotho and Botswana affected by HIV/Aids.

Ingrid Seward, the editor-in-chief of Majesty magazine and a royal biographer, said she thought the publisher, Penguin Random House, would be pleased with its focus on Diana.

“He’s got a very good ghost who will write well about feelings, and I think it’s totally fair that Harry should talk about his mother, because everybody else in the world has and they’ve sort of taken her over,” said Seward. “The publisher will know that Diana sells. And you don’t have to say too much — because whatever he says is coming from him.”

Spare will be one of the biggest books of 2023: as soon as it was available to order, in October, it reached No 1 on Amazon both in the US and UK, and has remained near the top of the British charts ever since. Dotti Irving, the literary publicist whose clients have included JK Rowling and who promoted the Booker prize for three decades, said: “What this book has — and this is integral to any really good PR campaign — is a very strong word-of-mouth element.”

This book is not even close to being the end of the “H and M” show, either. Alongside further projects for Netflix, the $20 million deal the Sussexes struck with PRH is understood to be for four books in total. The others are currently thought to be a wellness-focused tome by the duchess, a book about leadership and philanthropy, and potentially a Meghan memoir too.

“The overall impression is that this is a man who has never recovered from the trauma of his mother dying so young, and then along comes Meghan and he projects onto her a parallel with Diana.”

Moehringer is understood to have approached a number of Harry’s friends to research Spare, including his ex-girlfriends, although many are thought to have declined to speak. A significant portion toward the end of the book is also understood to be given over to criticism of the media, especially the British tabloids. Harry, of course, will have to engage with the much-maligned media to promote his memoir, although such interactions have been carefully curated.

The duke will give one major television interview to broadcasters on each side of the Atlantic. In the UK, Tom Bradby, who presents the ITV News at Ten and has known Harry for more than two decades, has landed the scoop. Bradby, 55, became close to both brothers while he was a royal correspondent in the 1990s, and his documentary revealed Meghan’s mental health turmoil. The interview is understood to have been recorded in California, and will broadcast on January 8, two days before the book hits the shelves.

ITV will have had to negotiate over the timings with the broadcasting giant CBS, which won the US exclusive and will take precedence. Of the two high-profile contenders to win the interview — the news anchor Anderson Cooper, who works for CNN but is also a correspondent for 60 Minutes on CBS News, and Gayle King, who co-hosts CBS Mornings — Cooper, 55, triumphed and his interview is set also to be broadcast on January 8.

Cooper, a popular presenter who as a member of the Vanderbilt family is almost American royalty himself, shares the couple’s passion for promoting conversations about mental health. He has a podcast about grief and loss called All There Is — his elder brother Carter killed himself in 1988, aged 23, and Cooper has spoken about how his death left his family, especially his late mother Gloria, with many unanswered questions.

King, 68, who is friends with the Sussexes and attended Meghan’s baby shower, was also a strong candidate; she has spoken out in defense of the couple, including over their decision to make the Netflix series, stating that it was not “a reality show”.

JR Moehringer is understood to have approached a number of Harry’s friends to research Spare, including his ex-girlfriends, although many are thought to have declined to speak.

Bradby, in particular, will be viewed by the duke as a safe pair of hands. “I think the American interview is driven by Random House and where sales will best be boosted,” said a broadcasting source. “Whereas in the UK, this is will be more about Harry thinking he wants the most straightforward, honest interviewer, and Tom has always played a straight bat. He has had this relationship with the two princes since they were children and remains very amicable with Harry, and one feels that he knows lots of things that he has never used to his advantage.”

The source added that Bradby has a difficult line to tread: “There’s a balancing act here: he has to be sympathetic — which comes naturally to Tom — but he also has to hold Harry to account and make sure he asks the difficult questions where ‘recollections may vary’ with other members of the royal family. And then there’s the fundamental question of why is Harry doing this? A lot of people, particularly among the older generation, will feel he should stay quiet about his family.”

The book will not have a newspaper serialization in the UK, with a source at PRH saying it felt unnecessary given “the book would sell without one”. Publishing sources say they expect him to give at least one newspaper interview; The New York Times, in which his wife wrote about her miscarriage in 2020, could be a potential home for it in the US.

However harsh the memoir’s criticisms of the royal family, the Sussexes are still expected to be invited to the King’s coronation on May 6. The royal family is also predicted to remain tight-lipped about the book in the hope of being seen to retain the moral high-ground, even if there will be considerable background briefing to the press.

“I think they’re just very cleverly saying nothing,” said Irving. “There’s nothing to be gained from washing the royal family linen in public.”

Spare, by Prince Harry, the Duke of Sussex, will be published on January 10 by Random House

Rosamund Urwin is the media editor for The Sunday Times