Princess Beatrice was wearing a blue and gold gown by British couture label Marchesa for her 18th birthday party.

BBC: Princess Beatrice at annual Garter service last month

And Zooey Deschanel went the princess route in a frothy pale blue Reem Acra ball gown.

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Meet the blue sapphire, gemstone of choice for biblical kings and the late Princess Diana, now de rigueur among legions of royal admirers and, more recently, high-end jewelers.

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