The Kate Middleton Effect: British Retailer Reiss Sees Profits Double Fashion The buying public still can't get enough of the Duchess of Cambridge's style. Kate Middleton's outfits have spawned countless knockoffs and sold out within days of her appearance in them. But the "Middleton effect" got backed by some empirical evidence last week when Reiss reported that the company increased sales and doubled operating profits from £4.3 million to £8.5 million ($6.7 million to $13.2 million) in 2011. The Duchess famously wore a white dress by the retailer for her official engagement photograph with Prince William, inspiring Reiss to re-release the simple shift, which then quickly sold out. Middleton later repeated the number in July on an official visit to Canada (see above), this time paired with a red hat and flag pin in honor of Canada Day. In May, Middleton wore a tan Reiss dress to meet President Barack Obama and Michelle Obama at Buckingham Palace. Along with Alexander McQueen, Issa and Jenny Packham, Reiss has quickly become one of the Duchess" favorite labels. And luckily for the brands, Middleton's favor has not only resulted in buzz about the companies, but big bucks, too. PHOTOS: Kate Middleton's Amazing Fashion Evolution