The Cholmondeleys live minutes from Prince William and Kate's Norfolk bolthole Anmer Hall in their own equally lavish mansion Houghton Hall, while the Cambridge children - Prince George, Princess Charlotte and Prince Louis - have been playmates of Rose and David's kids, twin sons Alexander and Oliver and daughter Lady Iris, for years.
Earlier this year, The Sun broke the story that William and Kate had "fallen out" with their high-society friends for an unknown reason, prompting Kate to order her husband to banish Rose from their suitably named social circle 'The Turnip Toffs' for good.
"No one understands quite how things have come to this. Over the years, Rose and Kate's lives have been entwined in many ways," a source told The Sun in March.
"It's well known that Kate and her former best friend Rose Hanbury have had a terrible falling out. They used to be close but that is not the case anymore."
So ruffled was the House of Windsor by the rumours, Prince William made the unusual move of threatening legal action against publishers.
The falling out is all the more intriguing given Rose and David's historic connection to the royal family.
Rose's grandmother, Lady Elizabeth Longman, was a bridesmaid at Queen Elizabeth and Prince Philip's royal wedding in 1947.
Her Majesty remained close with Ms Longman until her death in 2016.
Rose was also invited to William and Kate's 2011 wedding at Westminster Abbey, and the Cambridges were the star guests at a charity function held by the Cholmondeleys at Houghton Hall three years ago.