It was a moment of Cinderella magic: The future queen, emerging from a Rolls Royce in a slim ivory-and-white satin gown with a dramatic neckline, sheer lace sleeves and a train that followed her straight into fashion legend.

The dress, perhaps the most closely guarded secret of the royal wedding, became an icon from the moment it was broadcast around the world as Kate Middleton appeared at the doors of Westminster Abbey to marry Prince William.

Fashionistas swooned. Some people cried.

"It was perfect," gushed Darcy Miller, editorial director for Martha Stewart Weddings. "She looked incredibly beautiful, classic but also modern. And what's even more important, she looked like herself."

The palace went to extraordinary measures to keep the dress and its designer under wraps. It wasn't until Kate emerged from the car that it was revealed: Sarah Burton, creative director of the Alexander McQueen fashion house, was behind the long, lean gown, which hit the sweet spot between elegance and youthfulness, modesty and sensuality.

For the house of McQueen, the dress was a reversal of fortune beyond anything a Madison Avenue executive might have dreamed. A little more than a year ago, McQueen killed himself, and the industry wondered whether the label could survive without its brilliant but troubled namesake.

Uncounted hours of work went into the gown, fitted with a V-neck bustier and sweeping, eight-foot train in white and ivory satin gazar with a standup lace collar and long sleeves.

It was topped off by an antique Cartier tiara on loan from Queen Elizabeth II and a veil of tulle. It had the nipped waist and slightly flared hips that have come to be McQueen trademarks.

The ensemble was sleek and understated — particularly in comparison with the monumental gown Princess Diana wore at her 1981 wedding to Prince Charles, with its XXL puff sleeves and seemingly never-ending train. Its pared-down lines more closely recalled the simple elegance of the dress Grace Kelly wore when she married Prince Rainier of Monaco in 1956.

Observers praised Kate's choice as in step with the times and predicted the dress would launch a thousand knockoffs, just as Diana's had.

"This will have a huge impact on the bridal industry that will last for the years to come," said Jessica Michault, online style editor at the International Herald Tribune. "You are going to have women around the world wearing dresses that look as much like this one as possible."

Katherine Rabinow, a photographer from Houston who was in London for wedding day, captured the overwhelming approval among those who turned out for a glimpse of the young couple.

"It's a dress I'd love to see my daughter marry in — whether she was marrying a prince or not," she said.

In a statement, Buckingham Palace gave an exhaustive description of the dress, from the number of tulle-swathed buttons running down the back (58) to the technique used to craft the lace — Carrickmacross, which has its origins in 1820s Ireland.

So intricate was the gown's confection, the palace said, that the workers at the Royal School of Needlework who created the lace motif of flower, thistle and shamrock washed their hands every half-hour to keep the material pristine and used new needles every three hours to keep them sharp.

The statement said Kate chose the McQueen brand for "the beauty of its craftsmanship and its respect of traditional workmanship," and worked closely with Burton on the design.

Burton called working with Kate, who became duchess of Cambridge, "the experience of a lifetime."

"Catherine looked absolutely stunning today, and the team at Alexander McQueen are very proud of what we have created," Burton said in a company statement. "It was such an incredible honor to be asked."

In keeping with tradition, the ensemble included "something new," a pair of oak-leaf-shaped earrings with a diamond acorn suspended in the center, given to her by her parents, and "something borrowed," the Cartier "Halo" tiara from the queen.

The tiara was first purchased by the duke of York, later King George VI, for his duchess, who later became the Queen Mother Elizabeth. It was given to the current queen by her mother on the queen's 18th birthday.

Despite an overwhelming public appetite for details, the palace clamped down on any potential leaks, remarkably managing to keep everything a secret until Kate alighted at the abbey.

British media had tapped Burton as a top contender for the plum commission, but the designer repeatedly denied the rumors. Reports that parts of the McQueen office had been cordoned off to prevent prying eyes from getting a peek intensified the speculation.

When a photo was taken outside the Middleton family's hotel of a woman, her face obscured by an oversized trapper hat and her accessories looking suspiciously like those favored by Burton, it clinched the deal for some.

For the house of McQueen, the commission was a coup. Just over a year after his suicide, the brand has now been catapulted into the stratosphere of household fashion names like Chanel and Dior.

McQueen had been suffering from depression and took his life in February 2010 days after the death of his mother. The suicide shook the house to its foundations, leaving industry insiders to wonder how it could go on without him. Rumors circulated that the parent Gucci Group was contemplating shuttering it.

But some of those doubts were put to bed after Burton, McQueen's longtime right-hand-woman, showed her debut collection as creative director last October, a tour de force of structured, nip-waisted frocks in feathers, braided leather and what appeared to be delicate butterfly wings. With that collection, Burton proved she had what it took to step into the massive shoes of one of the world's most celebrated designers.

Since the royal engagement was announced in November, the fashion world had been crossing its fingers that Burton would be tapped. McQueen is among the highest-profile British labels, and industry insiders said the commission would be a fitting tribute to the late designer's legacy.

The editor of British Vogue, Alexandra Shulman, recommended Burton to palace officials when they queried her about the best choice to design Middleton's dress. Anna Wintour, the influential editor of the American edition of Vogue, also threw her weight behind Burton, praising the designer's "brilliance" during a recent visit to London.

Burton edged out a number of other high-profile British designers with experience in wedding gowns, including Vivienne Westwood, Bruce Oldfield, Alice Temperley and Philippa Lepley.

The wedding, which the British culture minister estimated would be seen by 2 billion people around the world, was cast as a showcase for British designers. Labels from outside Britain apparently did not receive serious consideration in the gown sweepstakes.

Following Friday's unveiling, industry insiders were already bracing for the wave of brides, from Boston to Beijing, clamoring for knockoffs of the long-sleeved lacy style as soon as manufacturers can rush them into shops.

"There's absolutely no doubt that Kate's dress will be a trendsetter," said Robb Young, author of "Power Dressing: First Ladies, Women Politicians and Fashion. "It's sleek, understated, flattering, thoroughly modern and romantic, which, ultimately, I think is probably what most brides today are looking for."

Even before the marriage, Kate emerged as a fashion plate, capable of launching new styles just by wearing them once. Inexpensive High Street copies of the blue dress Middleton wore for the November engagement announcement have flown off the shelves, and sapphire rings modeled on hers have challenged diamond solitaires for the title of most popular engagement rings.

Burton's work reportedly caught Middleton's eye when she designed an off-the-shoulder wedding dress for Sara Buys, a fashion journalist who married Tom Parker Bowles, the son of Prince Charles' wife, Camilla, in 2005.

Burton, who was raised in Manchester in northern England, joined McQueen in 1996 as an intern, working closely with the designer until his death. Unlike McQueen, whose edgy personality was well known, the 36-year-old Burton has largely shunned the limelight. She's not a player on the London nightlife scene, and even at the McQueen runway shows, she ducks out only briefly for a shy bow.

Burton has dressed A-list celebrities in the past, from Oscar-winning actresses Cate Blanchett and Gwyneth Paltrow to pop diva Lady Gaga.

"The choice of Sarah Burton shows Ms. Middleton has more spunk and independence than people suspected ... and so does that plunging neckline," said Christina Binkley, a style columnist for the Wall Street Journal. "It's going to be fun to watch these royals — not because I expect they'll be chased by scandal, but because they have a reassuring blend of class and ease and adventure. The dress is a great example of that."


Barchfield contributed from Paris. Cassandra Vinograd contributed from London.