Princes William and Harry "started quarrelling" at Prince Philip's funeral once they were back inside Windsor Castle, a royal author has claimed.
It had been hoped that the feuding brothers would reconcile after Harry returned to the UK for the ceremony to honour their grandfather, the Duke of Edinburgh, in April.
After the service, the pair were seen in conversation after 'subtly' being brought together by Kate Middleton.
But according to Robert Lacey, author of the book Battle of Brothers, they were unable to start repairing their relationship and began to argue as soon as they were away from TV cameras.
Writing in the Daily Mail, he said: "Those hopes were dashed within minutes of the siblings getting inside the castle and beyond camera vision. They started quarrelling again.
"'There they were, at each other's throats as fiercely as ever,' relates one long-time friend with a tired and helpless shrug.
"The rage and anger between those two has grown so incredibly deep. Too many harsh and wounding things have been said."
He added that he doesn't believe the conflict is likely to end any time soon.
On Thursday, the brothers will be reunited in public for the first time since the funeral for the unveiling of a statue in honour of their late mother Princess Diana at Kensington Palace on what would have been her 60th birthday.
Much attention has been focussed on them ahead of the event - after last month, Harry accused the royals of "total neglect" in his Apple TV documentary series, The Me You Can't See.
He also lashed out at his father Charles's parenting in the series and during an appearance on the Armchair Expert podcast.
But in his latest public appearance, Harry gave a nod to his older brother while paying tribute to young people's "humanitarianism" during an awards ceremony.
Speaking after yesterday's virtual ceremony for The Diana Award, which recognises those who create and sustain positive change, Harry said: "I'm truly honoured to be celebrating your work, your commitment to change-making and the vital role that you've taken on representing a new generation of humanitarianism.
"Later this week, my brother and I are recognising what would have been our mum's 60th birthday, and she would be so proud of you all for living authentic life with purpose and with compassion for others.
"Our mum believed that young people have the power to change the world."
