PRINCE William's rift with Harry is "the hardest thing he's been through" since their mum Diana died, a royal expert has claimed.
Author Duncan Larcombe said the Duke of Cambridge has endured an incredibly tough year and feels like "he has lost his brother and his best friend".
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The writer, who penned Prince Harry: The Inside Story, said the ongoing tension between the brothers began when the Duke of Sussex stepped down from life as a senior royal to move to the US with wife Meghan Markle.
Since then there have been more reported feuds - the most recent sparked by Harry and Meghan's tell-all chat with Oprah Winfrey.
Larcombe told : "There's no doubt this is one of the hardest things that William has gone through, the hardest since his mother died.
"He feels he has lost his brother and his best friend."
Meghan and Harry's televised interview with Oprah sparked a royal crisis, as several members of the family came under fire.
In it the couple alluded to Harry's rift with William, with him saying he loved his older brother "to bits" but that they were on "different paths".
It had previously been reported that the two brothers had barely spoken for more than a year after Megxit.
The Duke and Duchess of Sussex also told Oprah that a member of the royal family had asked what colour their then unborn son Archie's skin would be.
This was later confirmed not to be the Queen or Prince Philip - but the identity of the 'royal racist' remains unknown.
William was forced to , insisting: "We're very much not a racist family."
Prince Charles was also left "deeply hurt" after Harry claimed his father stopped taking his calls after Megxit and said there was a "lot of hurt" between them.
And Kate Middleton was reportedly "mortified" by claims she made Meghan cry during a wedding feud.
But William and Kate have stuck by one another amid the drama, it is claimed.
Larcombe said: "Kate has been William’s silent pillar of strength. They’re a double-act.
"It was always vital that William married someone who would strengthen his journey to the throne – and that is Kate.
"It’s business as usual for the pair of them, no matter what has been going on behind closed doors.
"Both William and Kate believe when you fall off the horse, you get straight back on and they don’t let anything effect their diaries and duty."
Despite the tensions, William and Harry will put on a "united front" at the unveiling of their mother Princess Diana's memorial statue, it has is claimed.
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The royal brothers are set attend the July 1 event despite reports they have barely spoken since the Sussexes' bombshell Oprah interview.
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Harry, 36, and William, 38, have collaborated on the design of the statue, which will be unveiled at Kensington Palace.
The date of the unveiling is what would have been Diana's 60th birthday.