No shame in that, either. Everyone else flaunts it, especially royalty, as she should know by now.
There is much precedent, but we could start with the Monaco girls. Princess Stephanie is well documented bare-breasted, and in a variety of cup sizes. The most recent set, implants that seem to be bowling balls she has commandeered from a local pensioner, were in thrusting evidence at her brother's wedding. They looked set to fall out of her dress any moment, and must have upstaged the bride.
Her more elegant sister, Princess Caroline, features naked from many angles on the internet, which her husband, a fellow aristocrat and rational man, would appreciate. He'd like that sort of thing because he reportedly had a fling with Miss Nude Belgium a while back. Wills needs to be more urbane.
Then there's his aunt, Princess Margaret, who was snapped by the paps years ago at her holiday shack with her much younger lover. I doubt she kicked up a fuss, though from memory the snaps were unflattering. An older woman will always be grateful to be seen to have pulling power.
For more recent precedent, Fergie, Duchess of York, was snapped having her toes sucked by a man who was definitely not the duke. That was also in France, where the better class of person gaily sheds inhibitions as Kate has done, quite likely under the influence of champagne - or in some cases a snort of something more expensive. Naked paparazzi pics of former president Jacques Chirac were taken there but never published, and we should be glad of that. Paunches are never going to cut it.
As for royalty flashing, there's no finer example than the duchess' brother-in-law, Prince Harry, a mere couple of weeks ago. We can look him up, too, on the internet, where he apparently bounces about in mating tackle, but I've seen too much of that sort of thing in my time to bother.
There is a comprehension problem with the world's media over incidents like these, which are quite understood by anyone who has ever mixed with former boarding school boys of the better class. They like nothing better than ripping their gear off, especially while drunk, and chundering on the upholstery.
I used to idly wonder at the homoeroticism of it all, but we shouldn't read too much into innocent fun. And that should be Kate's position. She's got the rest of her life to put up with it, so why spit the dummy now?