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The black see-through dress with a blue trim was bought by an unidentified buyer today in London. The auction price, which excludes a 20 percent buyers' premium, was originally expected to reach £8000.
Some commentators maintain that the dress played a role in sparking the royal romance that started shortly after the event.
It was initially intended to be worn as a skirt, but Middleton wore it as a short dress with black lingerie underneath.