We all know the royals love horse-racing, but it gets a bit tricky when you back the wrong nag.
Once upon a time, Princess Beatrice and her sister Eugenie chose to side with their fun, party-loving cousin Prince Harry, rather than stick with stick-in-the-mud William.
And now, amid the toxic fallout from the Jeffrey Epstein saga, that decision is coming back to haunt them.
Eugenie and Harry, in particular, have always been close - though not especially in age (she's 35, he's 41). As Omid Scobie wrote in his Sussex hagiography Finding Freedom: 'Of all the Queen's grandchildren, Harry and Eugenie have one of the most natural connections.'
They spent a lot of time in childhood together, going on holidays with his mum Diana and hers, Fergie.
Eugenie acted as Harry's matchmaker more than once, introducing him to Cressida Bonas, and she was also reportedly among the first to know about his relationship with Meghan Markle, whom she knew through a mutual friend.
She and her husband Jack Brooksbank 'double-dated' with Harry and Meghan in the Toronto 'early years', as well as in London, and she was the only royal to be praised in their shameless Oprah Winfrey interview.
Meghan is once said to have regarded her as a friend, insofar as she sees anyone as a friend.
So Eugenie and Beatrice have always been more Team Sussex than Team Cambridge.
Both York sisters, like Fergie, married well: Beatrice to Edoardo Mapelli Mozzi (left), a property developer; Eugenie to 'businessman' Jack Brooksbank.
Indeed, tensions between the princesses and William go at least as far back as 2011 when the now-heir to the throne failed to invite Beatrice's long-term boyfriend Dave Clarke to his wedding to Kate.
Now, their misplaced loyalties could see the women one day lose not just their shirts but their titles, privileges, status and cherished royal freebies.
The York sisters take after their parents - and not just in having an apparently wonky moral compass and a fondness for money.
Both gals, like Fergie, married well: Beatrice to Edoardo Mapelli Mozzi, a property developer; Eugenie to 'businessman' Jack Brooksbank.
Like their mother, they too enjoy being photographed in wacky outfits - hello, puffball skirts and hideous fascinators - despite knowing all too well the negative comments they'll receive online.
In truth, I've always liked their joie de vivre and Tigger-like exuberance - but, increasingly, I wonder if their gurning smiles mask a darker side.
I'm certain William gave the sisters the benefit of the doubt, as we all did, when it emerged a convicted paedophile and another sex offender (Jeffrey Epstein and the ex-Hollywood mogul Harvey Weinstein) had been invited to Beatrice's 18th birthday bash at Royal Lodge. I wager she barely knew half the names on the guest list.
'The princesses take after their parents - and not just in having an apparently wonky moral compass and a fondness for money'
But we and William now know that they were both adults - 20 and 19 - when they accompanied their grasping mother to visit Epstein in 2009, five days after he was released from prison and while he was under house arrest for child sex crimes.
Beatrice was also, apparently, key in persuading her doltish father to subject himself to Emily Maitlis's forensic Newsnight grilling in 2019. At the time, I thought she was just a daughter naively blind to her daddy's faults.
The young woman, I now see, was no fool. She must have suspected Dad was dodgy, but thought he should go ahead with the interview anyway. Did she really believe a word of his defences, including that nonsense about him being 'unable to sweat'?
Yet now we learn, thanks to the Epstein files, that Beatrice helped advise her mother on how to placate that monster following his anger after Sarah had called him a paedophile in a newspaper interview as far back as 2011.
And it was also revealed today that in December that year Andrew sent Jeffrey Epstein Christmas cards adorned with photographs of his daughters. To a paedophile!
The first card, dated December 21, 2011 and signed by the then Duke of York, wished Epstein, 'much joy and happiness at this time and for the year ahead'. The sisters are pictured smiling - Beatrice wearing a crown and Eugenie a fur hat.
I can only imagine that after these latest revelations in the Epstein files about the York sisters, with possibly more to seep under the door, that William and Catherine must be shuddering at the very thought of their cousins.
They hoped that Andrew, at least, had been dealt with following the stripping of his titles and his home, Royal Lodge - but now the prospect that his daughters were caught up in the murky affair too must be causing them anguish.
Catherine, in particular, will be appalled, given her commitment to the importance of early years safety.
Once William, far more ruthless than his gentle father, is King, will there be invites to the coronation, funerals or garden parties? Not waving from the balcony - but drowning in ignominy.
The only rubber ring that could possibly be tossed their way may come from Harry. Privately, perhaps, he's sympathetic to his childhood chums.
Embarrassed for Beatrice when reading her mother's email to Epstein about her own daughter's 'shaing' weekend. He knows what it feels like to make a mistake. He knows what it's like to learn your dad is far from perfect.
But Harry knows that Beatrice and Eugenie, however much he may like them personally, are tainted by their associations with their parents. He knows if he even touches these toxic links, they will poison him too.
The girls made a terrible choice: now they have to live with it.