Hell hath no fury like a sister upstaged - not least when she's a socially climbing Wisteria sister with a globally acclaimed rear-end. This week, we learnt that 32-year-old Pippa Middleton, sister of the Duchess of Cambridge, 34, is to marry her boyfriend, hedge fund millionaire James Matthews. Behold, the stage is set for a lifelong rivalry between old-money stuffy and new-money bling. Kate may have the prince, but Pippa looks set to have the ball.
Matthews, 40, is a scion of one David Matthews - a miner's child, like Ma Middleton - a former second-hand car salesman who set up the glitzy Eden Rock hotel in St. Barths in 1995.
A chip off this fabulously nouveau riche block, James is vastly wealthy in his own right, boasting a £17m (NZ$31m) London mansion and £3m private jet.
It's been reported that, in time, Pippa could even acquire a title: the suitably racy sounding "Lady Glen Affric", bought (bought!) when her future father-in-law purchased a Scottish estate back in 2008.
James's mother is artist Jane Parker, his brother Spencer a reality television star famed for sleeping with over 1000 women by the age of 27.
The announcement of this next Middleton marriage is wonderful news for Carole, as she'll now have people to look less nouvey next to.
Kate is said to be "absolutely delighted". One wonders whether this might be a euphemism for "absolutely pea green", as the disparity between the sisters' future lives becomes ever more apparent.
Here is our guide to how their chosen tribes roll and how this rivalry may play out:
Largely locked in the family vaults. OM gals inherit their engagement rings: witness Kate's acquisition of Diana, Princess of Wales' 80s-tastic Ceylon sapphire.
New Money: Pippa's rock is mighty: a 4-carat, asscher radiant diamond number estimated at £200,000.
One might have hoped for a crass conker but, in fact, it is swooningly lovely; off-piste in its Art Deco guise in a way that Kate had no option of being.
Still, given the Christmas tree effect that NM doyennes tend to favour - gold goes so well with the leather of one's tan, darling - expect decades of disco sparkle ahead.
Old Money: Kate does her own make-up and is expected to age gracefully. Her only rebellion against OM restraint is big hair (Diana did this too, young people!). Off-duty (she's never off-duty) she adopts yachting chic - as in Cowes - meaning Breton T-shirts and jeans. Her scrubbed-up guise will demand British designers and a pitiable number of L?K Bennett beige courts.
New Money: All-year face frying means NM is never averse to a little help: injectables from one's 30s, early lift at 40, everything going after 50. Off-duty (she's always off-duty) she adopts yachting chic - as in Monte - meaning Cavalli kaftans and gold wedges. Her scrubbed-up guise will feature the "full Gucc" - 90s speak for head-to-toe designer - but never current Gucc, darling, far too arty farty.
Old Money: He may look like his mother in his teens, but, from 25 onwards, the bald patch/equine teeth aspect dominates, and he will resemble his insalubrious uncles.
New Money: Sporty until his 40s, the NM chap dresses that bit too well, and will start going disturbingly Philip Green in middle age. This is fine - he'll be sleeping with someone else, anyway.
Old Money: Bunting, mugs, tasteful frockage, bride in dodgy eyeliner.
New Money: Lighting effects, tacky guests, dress that shows off one's figure, bride a shade of teak.
Old Money: OM refers to its "house" - even where "house" means a palace - one in town, more in the country. They also have access to their parents' and grandparents' houses. When someone dies, everyone moves up a house.
New Money: NM refers to its "homes" plural, a series of over-designed pads in global party destinations, including a (rarely occupied) London "base". They are forever amassing more, yet enjoy hotels, not least the ones they own. Homes are over-heated with everyone going barefoot.
Kate's watch is what the jet set refer to as "entry-level" Cartier - nouve code for "basic b****". A gift from William a couple of years ago, it is worth £4850. Think: modest, dependable, unshowy; like Argos.
New Money: Pippa's wrist candy is pure Barbie, were Ken fantastically vulgar: diamond-studded in pink gold (obviously), it costs £14,500. Some might say that investing in the same timepiece at three times the price was an attempt at sisterly top trumping.
We couldn't possibly comment.
Old Money: OM harbours a peculiar taste for faux middle-class entertainments such as take-out in front of the telly - basically, anything Nanny would have frowned upon.
New Money: NM romance involves public displays of affection, such as being flown somewhere to do something exorbitant in front of fawning admirers. Publicity is all.
The aim is that offspring could be mistaken for their parents, grandparents and great-grandparents, going back to 1837 - complete with bloomers, side partings and wonky ears. Riding is key, education purely optional.
New Money: NM nippers grow up fast with perma-tans, American teeth and Kardashian wardrobes. The phrase "school of life" will be thrown around, meaning an ability to make money and handle sex scandals. Skiing is key, education actively frowned upon.
Old Money: Don't strictly work, thus never strictly holiday, which is not to say they don't travel.
New Money: Occupy a state of rolling holiday.
Old Money: The Queen - matriarch, hard working, gives good brooch.
New Money: Princess Margaret - good-time girl, hard living, gave great kaftan.
The two clans rub up against each other a lot. OM needs NM for its infinite moolah, NM requires OM to take the glint of its brass. Kate will know how to treat her new relatives by the way some may have - a mite disdainfully, but seeing the need.
Meanwhile, Mrs Middleton can feel extremely satisfied in having both daughters married off in a way that fulfils her epic maternal ambition.
Now if only something could be done about brother James...