The Duke of Sussex’s new memoir, billed as a book of “raw, unflinching honesty”, will be released in the new year.

Spare, a reference to the phrase “the heir and the spare”, had been due to hit bookshelves this autumn but it will now be released globally on January 10.

There has been speculation that the date was pushed back as a mark of respect following the death of the Queen last month.

The memoir, published by Penguin Random House, promises to “take readers immediately back to one of the most searing images of the 20th century: two young boys, walking behind their mother’s coffin as the world watched in sorrow - and horror.”

“With its raw, unflinching honesty, Spare is a landmark publication full of insight, revelation, self-examination and hard-won wisdom about the eternal power of love over grief,” the publisher said.

The Royal Family could be faced with damaging newspaper headlines if Prince Harry chooses to delve into the most controversial elements of royal life from past decades, with Buckingham Palace likely to be steeling itself for revelations that could be detrimental to the monarchy and the Duke’s father Charles, now King and in the early stages of his reign.

When the deal to publish the book was first announced last year, the Duke of Sussex said: “I’m writing this not as the prince I was born, but as the man I have become.

“I’ve worn many hats over the years, both literally and figuratively, and my hope is that in telling my story - the highs and lows, the mistakes, the lessons learned - I can help show that no matter where we come from, we have more in common than we think.”

A spokesman for the King declined to comment.