Kate Middleton's "Duchess Effect" on Fashion

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In the past year, Kate Middleton has become a wife, a Duchess and, now, a certified fashion icon with real market power.

Reiss, a clothing line favored by Middleton for her public appearances, saw its profits skyrocket this year, enough that the power of Middleton's fashion choices has been dubbed " The Duchess Effect."

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When Middleton, the wife of Prince William, stepped out in a $340 camel-colored dress from Reiss to greet President Obama and the first lady in May, traffic on the Reiss website rose by 200 percent and the dress quickly sold out.

One month later, the $310 Peacock dress the 29-year-old wore to the Epsom Derby was up for sale on Ebay, for $1000, just hours after it was spotted on the Duchess.

Just like that, Reiss's profits rose too.  The family-owned, British retailer's operating profits rose from around $6.6 million to $13.2 million, according to filings at Companies House in the U.K.

Reiss's sales also jumped, from $120.3 million to $135.6 million, and its pre-tax losses were converted to a profit of $5.6 million.

"She really is the every girl, and I think that's what's so inviting about her," Joe Zee, creative director of Elle magazine, said of Middleton's appeal.

The fashion frenzy swirling around Middleton began even before she and William, also 29, tied the knot in April.

The Reiss Nannette dress she wore in the couple's official engagement photo was already sold out by the time the Mario Testino-photographed pictures were released in December 2010.   Demand for the $245 dress was so high, the chain re-released the dress, only to sell it out again, at a rate of one dress sold every minute, the UK's Daily Mail reports.

Reiss, which has 114 shops in 14 countries, is typical of the low-key approach Middleton has brought to her royal wardrobe.

In September, the Duchess of Cambridge, as she is formally known, was spotted on a $170 shopping spree at her local Topshop, on Kensington High Street.  She is also said to have turned down the entourage of stylists and servants that typically accompany royal life, preferring to make her own fashion choices.

"I don't need her to break new rules in the world of fashion," Elle magazine's Zee said.  "I just need her to look gorgeous and happy and that's what she looks."