According to one royal book, a small group of mutual pals shared by William and Harry have spent three years attempting to ease tensions between the two.

However, according to Robert Lacey, author of the shocking book Battle Of Brothers, the schism between Harry and his brother William is unlikely to be healed anytime soon.

Lacey writes that the friends “frequently discuss how to heal the breach — though with an increasing sense of despair.”

But the former Hollywood star’s “endless PR” spin makes a quiet reunion that many palace insiders are hoping for difficult.

In the Daily Mail, he wrote: “All the mutual friends I have encountered find themselves seeing both points of view — William’s defensiveness of the monarchy as he sees it, and Harry’s defensiveness of his wife.

“Love versus duty. This is what makes it so painful. The friends commiserate with each other over the tragedy they are witnessing, and they frequently discuss how to heal the breach — though with an increasing sense of despair.

“Sussex supporters have noted the bizarre combination of self-promotion and self-pity that seems to characterise Meghan, and can see why it has infuriated William.

“‘Meghan can be a 500 percent nightmare,’ some close friends of Harry are among the first to admit. ‘The never-ending PR. She’s just so . . . American!’

“On the opposite side, friends of William and Kate are willing to concede the jealousy the Cambridges once felt at being overshadowed by the megawatt younger brother and his wife.”

According to Lacey, Prince William will have no option but to “swallow his pride and smile” beside his sister-in-law Meghan on the Platinum Jubilee balcony next year.

He continues: “According to one of my sources, it’s been pointed to him that everyone has a difficult sister-in-law.”

“William’s response was to nod his head in sage acceptance. Then suddenly he broke out angrily. ‘But look at the way that bloody woman treated my staff — merciless!’”

Lacey also claims that Harry has told friends that he wants to bury the hatchet with William and is prepared to accept some of his faults.

However, he is said to be as protective of his wife as ever, and the Kensington Palace bullying investigation is a persistent source of annoyance.

Jason Knauf, who worked in communications for both the Cambridges and the Sussexes, compiled a list of purported grievances from members of the combined household’s employees.

Lacey says William was “appalled” by the charges, which purportedly confirmed that “Meghan was fundamentally hostile towards the royal system”

“The duchess is saddened by this latest attack on her character, particularly as someone who has been the target of bullying herself and is deeply committed to supporting those who have experienced pain and trauma,” Meghan’s spokesman said at the time the claims of bullying were made public.

Her Majesty the Queen has agreed to foot the bill for the bullying investigation, according to a royal source: “There is no Sovereign Grant money spent on this review. It’s private. It is met privately. It’s not public money.”

It comes as Harry prepares to rejoin with William after returning to the United Kingdom for the dedication of a statue of his late mother, Princess Diana.

He is set to self-isolate at Frogmore Cottage in Windsor for five days before reuniting with William, 39, at Kensington Palace on what would have been Princess Diana’s 60th birthday on July 1.