Who made this dress?

Blair wore this dress in an episode of Gossip Girls, during a Hamptons White Party. Who is the designer I should have his name! Thank you in advance! http://buzzsugar.com/gallery/563775?page=0, 5.0

It was Serena and the designer is Oscar de la Renta http://teamsugar.com/group/1816741/blog/1898027

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