Auction house Sotheby's expects the dress to sell for up to $300,000 (Ā£220,000) when it goes under the hammer on 9 December.
She made a last-minute wardrobe change before heading out to the event, setting aside a less striking Valentino gown in favour of the off-the-shoulder dress with an asymmetric hemline and chiffon traā¦ [+117 chars]