"This was a conversation about where they were heading after ten years and they both agreed to go their separate ways for a while to try to work out what they want," said one source close to the family.
"I think it might be a William and Kate-type split [the couple split briefly in 2007] - I wouldn't be surprised if they got back together. They are both open to that. As we all know, there are several types of split, and this is of the most amicable kind, with no one else involved. It's just they felt it was decision time.
"Her family are very supportive of both of them, very fond of him and very open-minded about them getting back together. She is staying in the US and not coming back here. They are both terribly upset at the moment."
Without revealing who exactly prompted the break-up, the friend said: "They are two people who met quite young and have dated for a long time, and want to think hard about what they would like to happen."
Another friend of the family worded it thus: "Any prospect of an engagement had long passed its sell-by date, though a split can shift that feeling. So she is a footloose singleton once more - not a status she is relishing, despite the shedloads of party invitations."
Beatrice was introduced to Dave when she was 18 by her cousin, Prince William, at a party in 2006, hosted by Sean Brosnan, son of movie star Pierce.
William and Dave had become friends while studying at universities in Scotland - William at St Andrews and Dave at Edinburgh.
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Six years her senior, Dave is the son of multi-millionaire American lawyer Michael Clark, former chief legal counsel at Cadbury Schweppes, and his wife Carol. Dave has dual U.S. and British nationality and has spent much time in England.
His family moved to London when he was five and set up home in a £5 million pile in Hampstead.
After school, he returned to the States to attend preppy Bowdoin College in Maine, and spent a year at Edinburgh as part of his course.
A year or so later, he had his first proper job - in London, working for Virgin Galactic, Richard Branson's ill-fated attempt to open up space travel to the super-rich.
Dave was head of Astronaut Relations there for more than nine years and, in 2015, left to work for Uber, the controversial smartphone taxi network, where he is senior adviser to the CEO and head of external affairs.
Throughout Beatrice's time at Goldsmiths, University of London, they had been all but inseparable.
He was always at her side at Wimbledon, at Ascot, at parties, at film premieres, on holidays all over the world and with her parents at the ski chalet in Verbier.
His role at Uber saw Beatrice leave London last year and move to New York to be with him. Some who knew the Yorks have speculated Beatrice's parents, notorious freebie hunters Prince Andrew and Sarah Ferguson, would have preferred her to marry into a bit more money than Dave.
But others say this is patently not the case: "Of course, Beatrice is a Princess - Dave would feel the need to be successful to marry her. But Dave is from a very well-off background, anyway.
"Jack Brooksbank, Eugenie's boyfriend, isn't a high earner and is still establishing himself. Her parents don't mind at all."
Indeed, Fergie is said to be very upset by the split and had come to view Dave as a son.
Yet their path hasn't always been smooth.
In spite of having made the initial introduction, William had cooled his friendship with Dave, seeing him as "indiscreet", to the extent that he didn't ask him to his wedding in 2011 - a decision that hurt Beatrice very much.
Still, his exuberant personality, in contrast to the privacy-obsessed Royals, was something Fergie in particular relished. 'She adored him,' says one source. However, Dave and Beatrice's lifestyle, enviable as it looked, brought its own problems, too.
In the past couple of years, Beatrice had taken the flak for having gone on 18 holidays in less than two years.
Some close to the Royals felt Dave couldn't resist a good invitation, and Bea, the less confident of the pair, couldn't say no to going with him. The problem with dating a royal, as Kate knows, is there is always the suspicion of social climbing among some of their circle.
So when it became obvious that Dave relished the high life, with Beatrice at his side, some eyebrows were raised.
Others say this was grossly unfair: "Tech companies love their employees to be well-connected and at both Virgin - where he had to persuade celebrities to buy tickets into space for publicity reasons - and Uber, as external relations, Clark needs to network."
But that has had its own repercussions. It emerged last week that Beatrice had left her full-time job at Sandbridge Capital, an elite New York finance house, in order to set up some kind of consultancy backed by them.
It was her fourth job in five years, leading to accusations of her being workshy.
The first suspicions that all wasn't well with Bea's job came earlier this year when, rather than toiling away in Sandbridge's offices on the 23rd floor of the Trump Tower on New York's 5th Avenue, the Princess spent six weeks in the UK.
She was nominally here to attend her grandmother's birthday celebrations, but crammed in plenty of other fun, too.
In May, she attended the wedding of Lord Lovat to Petra Palumbo, her godfather's daughter, as well as the Chelsea Flower Show, a Mayfair fancy dress party and a concert at Windsor for her grandmother. But friends insist that the portrayal of her as someone who prefers deck life to desk life has been unfair.
"Like any girl her age, she's still working things out," said one. 'It's just that she has to do it in public. The idea that she's lazy is simply not true. She wants to work in finance and luxury brands."
Indeed, her academic career was notable for diligence. Head girl of her school, St George's Ascot, she battled dyslexia, yet passed her A-levels with an A and two Bs before going on to get a 2:1 degree in history and the history of ideas from Goldsmiths.
"After all, she does plenty of charity work - with the English National Ballet, Forget Me Not Children's Hospice, the Helen Arkell Dyslexia Centre, the Teenage Cancer Trust and others. She is a good-natured, kind person."
Whether, in due course, her ex-boyfriend will look back and realise how much he's missing and rekindle their relationship remains to be seen.
