Blake Lively, former princess of the Upper East Side, decided to dress as another princess at the Cannes Film Festival's premiere of Slack Bay (Ma Loute) this evening, with the help of Vivienne Westwood Couture. Take in her Cinderella gloriousness in all its detail, from the jewel flower-embellished front:

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Neat bow tying her ruffled cupcake skirt in the back:

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Crystal hair flower hanging right above her neck:

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And hint of a silver heel, Serena van der Woodsen's choice glass sipper:

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This is not her movie premiere, but it is her ball.

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