The book, which is currently being serialised in the Daily Mail, also claims the Sussexes were “rebuffed” by Buckingham Palace when they asked them to back up their claim publicly.
The book reads: “One privately [member of palace staff] recalled that Elizabeth II had been ‘as angry as I’d ever seen her’ in 2021 after the Sussexes announced that she had given them her blessing to call their baby daughter ‘Lilibet’, the queen’s childhood nickname.
“The couple subsequently fired off warnings of legal action against anyone who dared to suggest otherwise, as the BBC had done. However, when the Sussexes tried to co-opt the Palace into propping up their version of events, they were rebuffed.”
Shortly after Lilibet’s name was announced, the BBC reported a palace source saying that the Queen “was not asked by the Duke and Duchess of Sussex about naming their daughter Lilibet”.
As a result, the couple accused the broadcasters of libel but according to Mr Hardman the threat of legal action “evaporated and the libel action against the BBC never materialised”.
At the time, Harry and Meghan’s spokesperson said: “The duke spoke with his family in advance of the announcement, in fact his grandmother was the first family member he called.
“During that conversation, he shared their hope of naming their daughter Lilibet in her honour. Had she not been supportive, they would not have used the name.”
Lilibet was the childhood nickname of the late Queen which was reportedly only used by her parents, Princess Margaret and Prince Philip, and a few close friends.
Mr Hardman is best known for his work on the Royal family. He has worked for the Daily Mail since 2001 and wrote the book, Queen of Our Times.
Other revelations in the book include a new insight into Harry’s relationship with his father, King Charles.
It says that while the King was “extremely sad” about Harry’s estrangement, he now feels as though “he has done what he can and now he is King, there are many more things to think about”.
However, the book also quotes a senior official as saying Charles will “always” leave the door open for his youngest son.
The book also says that neither King Charles nor Prince William have read Harry’s memoir, Spare, but staff have informed them of “key points”.
The Independent has contacted Buckingham Palace for a response to the book’s revelations.