Is Kate Middleton Doomed?

It was supposed to be a private lunch, just Kate Middleton and her soon-to-be step-mother-in-law, Camilla, Duchess of Cornwall. A pre-wedding chat about catering and placements. But the paparazzi were tipped off and as she left The Berkeley hotel in London Kate must have felt the weight of her future life; its ceaseless scrutiny; the bizarre expectations.

Was her eyeliner too heavy, asked the next day's papers. Was that Diane von Furstenberg dress mismatched with her Whistles jacket? Would Prince Charles be appalled she ate foie gras, which he's banned from Highgrove? Did she laugh too raucously, talk too loud?

And crucially those legs of hers, long and lean in opaque tights, are they too thin? Let's compare with an old snap of teen lacrosse captain Kate. Yes, definitely skinnier now. But is there cause for worry, for food-disorder speculation? Maybe not yet. But let's line up a few anonymous "friends" to dish, post-honeymoon perhaps, on "Troubled Kate"?

Oh Diana, your silvery shadow flickers always behind the girl your son will marry. As Kate stepped out for her engagement photo, in the Princess of Wales's diamond and sapphire ring, women shuddered. The Ring of Doom! The symbol of loveless marriage, epic loneliness and an early end in Paris's Alma Tunnel. But poor William had carried that ring around Africa in his little backpack planning to propose. To him it signified the union between the parents who'd borne him, not a bad-fairy curse. But was it meekness that made her accept it? Or a certain chutzpah, a confidence that wearing Diana's jewellery didn't mean she was destined to share her fate?

Since she died nearly 14 years ago, no-one has matched Diana's ability to shift product. From a tabloid to a glossy magazine, her cover image guaranteed a sharp spike in sales. Hers was an ever-evolving story refracted in silent-screen-star eyes. Innocent teenage Diana betrayed by her prince, traduced by his icy family. Intuitive, scheming Diana who held the hands of the dying while she blew wide the palace doors. Tragic Diana, whose death to some will never be an accident.

And so a vacancy occurred. "Suffering Diva," the ad might read. "Must have wealth, weight fluctuations, vast wardrobe and hopeless love life." A few auditioned. Victoria Beckham had the glamour, the faithless bastard, the body "wasted with grief". Brad/Jen/Angelina had "there were three of us in this marriage" potential. Sure, all made us feel better about our humdrum nine-to-five: that no amount of Jimmy Choos can guarantee happiness. Yet no-one has matched the global reach, emotional range, operatic grandeur, dynastic implications - the sheer class of Diana.

So can Kate fill that vacuum left by the mother-in-law she never met, but who'll haunt her for the rest of her life? Certainly the camera loves her just as well. She has that same ability - perhaps the sole skill required of a female royal consort - to look good wearing anything. Country casual, military, polo, Christmas at Sandringham: she always rocks the outfit. A Buckingham Palace Barbie.

And, in this, Kate exceeds gauche, fumbling Diana experimenting with her pie-crust collars and unintended flashes of décolletage. Because here lies the difference: Katy waited.

She may have been mocked for all these years since the University of St Andrews where she met William, putting her life on hold, frittering it away in pretend jobs or listless stints at the family party accessories firm, slowly reeling in her prince. But all the while she was at "Princess Finishing School", taking modules in dress sense, how to smile and wave, look grateful and gracious, how to be a princely companion rather than upstage William on walkabouts. (And above else work out whether this royal life was worth having.) Until finally, at 29 years of age - the oldest spinster ever to marry a future king - she has graduated summa cum laude.

Diana's problem was the royal family assumed she would just know how to be a princess. Raised on a grand estate, she mixed with Charles as a child, courtiers and courtesans were in her lineage. She was born to be royal. But Kate's ordinariness is her strength. Her parents are in trade, their millions came from plastic cups and party poppers. Quelle horreur! Her grandfather was a miner. Her mother, Carole, a former air stewardess, is nicknamed "doors to manual" by some of William's pals. Yet since no-one expected Kate to have a clue about royal duties, she's had untold guidance, while Diana - a decade younger when she married - was expected to cope alone.

Besides, the secret of being a beloved princess - as Diana was the first to deduce - is less about blue blood than media management. And who better to master that than a modern girl? Who is more equipped to withstand the vicissitudes of public life than a woman whose family shinned up the social class tree in two generations? How much more useful to be a smart woman with a university degree, than someone who described herself as 'thick as a plank"? Better a girl with a solid, boringly ordinary family than one run through with alcoholism, coldness, neglect and familial desertion. Better a woman who knows about love and men, than a doe-eyed virgin.

Yet the greatest barrier to Kate suffering Diana's fate is her chosen prince. Charles revels in formality and protocol and loves his multi-butlered, bespoke-suited royal life. William only wants a properly useful job as helicopter rescue pilot, no servants, no fuss, just a kind companion to share his "dirty sense of humour". His idea of luxury is to be ordinary: in that he is his mother's son.

While Kate faces the life of a royal wife, has her dresses dissected, her figure pulled apart and, in time, her parenting decisions harshly debated, she will have the consolation of a man who loves her. This is Diana's wedding present to Kate.