Royal expert Simon Heffer talked about the release of Prince Harry's memoir and how it could make or break his relationship with the royals, especially with his brother Prince William and father, King Charles III.

In his article for The Telegraph, the royal commentator said that the monarch's response to his son's memoir will show how good a monarch he is. He said there is "great private concern" about how the memoir will impact His Majesty's reign and the reputation of the royals.

While Buckingham Palace has yet to comment publicly on the book, Heffner claimed that it has caused concerns in the "upper echelons" of the British Royal Family. This includes Prince William, who he said "is appalled at his brother's general behavior" and is in disbelief that the memoir is coming out at all.

The royal expert cited an acquaintance of the Prince of Wales who said that he can be "self-righteous and spoilt." But "there is no doubt he has the best interests of The Firm at heart in deploring the Duke's conduct."

As such, Heffner thinks that there may never be a reconciliation between Prince William and Prince Harry if "Spare" tarnishes the image of the British royals or The Firm. He cited courtiers who say they are "less convinced that the Prince of Wales would accept a reconciliation" which could cause a problem for their father.

King Charles III, on the other hand, could welcome the Sussexes back to the royal fold and allow them to live permanently in the U.K. That is unless "the book is indeed deeply damaging, in which case bridges may finally have been burnt."

Heffner added that the moment when His Majesty "comes at last to read his younger son's book is likely to be by far the most challenging of the year ahead. His response to it will demonstrate not just how good a father, but how good a King, our new monarch is."

Prince Harry's memoir, titled "Spare," will hit shelves on Jan. 10, 2023. His publisher, Penguin Random House, said the book contains "intimate, "raw and unflinching" accounts of the duke's life.

Prince Harry and Prince William
Prince Harry and Prince William Getty Images/Gareth Fuller