The 'Fab Four' spit when Prince Harry accused his brother Prince William and sister-in-law Kate Middleton of failing to support Meghan Markle, it is claimed.
It allegedly led to a "showdown" which saw Harry, 34, read the "riot act" to the Duke and Duchess of Cambridge after their children had gone to bed.
Meghan, 38, kept a "stony silence" during Harry's speech, which took William and Kate by surprise, it is claimed.
It is said the Cambridges assured Harry they were happy to offer more support to former Suits actress Meghan, and Kate even brought flowers to Harry and Meghan's home the next day.
The Duchess of Cambridge also offered to go to Wimbledon with her new sister-in-law following Harry's "riot act" speech last year, according to the Mail on Sunday, which reported the claims, citing unnamed sources.
Some sources claim the two families are still drifting apart, the report added.
A royal source told Mirror Online the claims were "nonsense".
A spokesperson for the Royal Family declined to comment.
In recent months the Duke and Duchess of Sussex have moved away from Kensington Palace, split from William and Kate's royal household and left the foursome's charity to start their own.
Meghan and Harry have also set up their own Instagram account, which now has 9.3million followers, just half a million shy of William and Kate.
Buckingham Palace and Kensington Palace have repeatedly denied allegations of a rift or a feud between the couples.
They were dubbed the 'Fab Four' following their first public appearances together.
This summer, Meghan and Kate attended Wimbledon together for the second year in a row.
In other royal news, the Queen has privately said that and its "inability to govern correctly", it is claimed.
And Meghan is fighting to stop scammers using her name to sell diet pills online, according to an exclusive Sunday Mirror investigation.
