Prince William 'must accept terms' before King Charles can enter crunch talks with Prince Harry

Harry's relationship with his brother has deteriorated over the last few years after the Sussexes unleashed several public attacks on the Royal Family.

Robert Hardman has claimed that reconciliation between Harry and senior members of the Royal Family will not work unless an agreement with Prince William is struck.

Hardman said: "Whatever the King does needs to be done in tandem with both brothers, not just one.

"He can’t have unilateral discussions if William isn’t in agreement."

The royal author added: "Whatever reconciliation or bridge-building happens, it needs to be a three-way process.

"People keep asking about the king’s feelings, but William also has to be on board, which adds complexity."

The Duke of Sussex's publication of intimate details regarding his relationships with Royal Family members including the Prince and Princess of Wales, in his memoir Spare "breached trust" with William, according to the royal author.

Hardman said: "The bond between the brothers historically runs deep.

"While we don’t see the full picture, we know they’re both very private.

"Some might wonder why Harry wrote a book [his memoir, Spare] if he values privacy, but there’s still much they keep private.

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"This is why William was upset by the book—not because of specific depictions, but because of the breach of trust.

"Things that happened between the siblings were made public, which is a huge deal for someone who values privacy like William."

Prince Harry and the Prince of Wales last saw each other at their uncle's funeral in August.

However, according to sources the brothers did not interact during the event.