Left: Rihanna at the 2011 BRIT Awards in February. Right: Author J.K. Rowling at the premiere of Harry Potter and the Deathly Hallows Part 2 on Thursday.
Both ladies wore different versions of the same Oscar de la Renta dress in London, but we want to know what U think!
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[Image via TIMMS-MARINER/XposurePhotos.com & WENN.]