Prince William lost his temper at Meghan Markle over her "merciless" treatment of her staff, calling her "that bloody woman", a royal expert has revealed.
The claim comes from author Robert Lacey in his book Battle of Brothers, which chronicles the rift between William and Harry, reports The Sun.
Lacey wrote that the feud between the "bitterly divided" brothers "does not seem likely to end any time soon".
But he wrote that William will have to "swallow his pride and smile" alongside his sister-in-law when they reunite next year for the Queen's Platinum Jubilee.
"According to one of my sources, it's been pointed to him that everyone has a difficult sister-in-law," he wrote for the Daily Mail.
"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!'"
But supporters of the Sussexes have also acknowledged that Meghan and William don't see eye-to-eye.
"Sussex supporters have noted the bizarre combination of self-promotion and self-pity that characterises Meghan, and can see why it has infuriated William," Lacey said.
"'Meghan can be a 500 per cent nightmare', some close friends of Harry are among the first to admit."
And he claimed the Duke of Cambridge was "instantly furious" when he found a "Dossier of Distress" that had been put together by Kensington Palace's head of communications Jason Knauf, according to the Sun.
In the new edition of his controversial book Battle of Brothers, Lacey alleges that royal staff felt "humiliated" by Meghan and Harry.
One aide recalls in the book, "I overheard a conversation between Harry and one of his top aides. Harry was screaming down the phone."
It all comes as Harry, 36, has landed in the UK ahead of the unveiling of Princess Diana's statue next week.
He was last in Britain when he came home to attend his grandfather Prince Philip's funeral in April.
Harry was seen chatting to William on the walk back from the ceremony at St George's Chapel. Meanwhile, his father Charles was seen leaving with William from exits near Frogmore Cottage where Harry was staying, two hours after the funeral.