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Open Image ModalTwins Mary-Kate and Ashley Olsen with their younger sister, Elizabeth. (credit:Getty)
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Open Image ModalAshton Kutcher and his twin, Michael. (credit:AP)
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Open Image ModalGisele Bundchen with twin sister Patricia (R), and sister Rafaela. (credit:Getty)
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Open Image ModalTwins Karen and Kate Elson. (credit:Getty Images)
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Open Image ModalScarlett Johansson and twin brother, Hunter. (credit:Getty)
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Open Image ModalTwins Charlotte and Samantha Ronson. (credit:Getty)
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Open Image ModalTwins Alanis and Wade Morissette. (credit:AP/WadeMorissette.com)
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Open Image ModalTia and Tamera Mowry. (credit:AP)
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Open Image ModalJoel and Benji Madden. (credit:AP)
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Open Image ModalTwins Kiefer and Rachel Sutherland. (credit:Getty)
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Open Image ModalTwins Aaron and Angel Carter. (credit:Getty)
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Open Image ModalTwins Dylan and Cole Sprouse. (credit:Getty)
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Open Image ModalTwins Jon and Dan Heder. (credit:Getty)
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Open Image ModalTwins Aaron and Shawn Ashmore. (credit:Getty)
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Open Image ModalTwins Tiki and Ronde Barber. (credit:Getty)
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Open Image ModalTwins Jason and Jeremy London. (credit:Getty)
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Open Image ModalTwins Barbara Pierce Bush and Jenna Bush Hager. (credit:Getty)
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Open Image ModalSandra Vergara, Sofia\'s sister. (credit:Getty)
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Open Image ModalLady Gaga and Natali Germanotta. (credit:Getty)
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Open Image ModalKate and Rooney Mara. (credit:Getty)
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Open Image ModalAnne Hathaway\'s brothers Thomas and Michael. (credit:Getty Images)
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Open Image ModalHaylie and Hilary Duff. (credit:Getty Images)
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Open Image ModalMarlon and Shawn Wayans. (credit:Getty Images)
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Open Image ModalEmma and Alex Watson. (credit:AP)
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Open Image ModalBlake Lively\'s older brother, Eric. (credit:Getty)
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Open Image ModalBeyonce and Solange Knowles. (credit:Getty)
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Open Image ModalBritney Spears\' older brother, Bryan. (credit:Getty)
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Open Image ModalMichelle Pfeiffer\'s younger sister, Dedee. (credit:Getty)
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Open Image ModalSienna and Savannah Miller. (credit:Getty)
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Open Image ModalBriana and Kaley Cuoco. (credit:AP)
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Open Image ModalMonica and Penelope Cruz (credit:Getty)
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Open Image ModalAdam and Michael Levine. (credit:Getty)
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Open Image ModalAudrina and Casey Patridge. (credit:Getty)
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Open Image ModalZooey and Emily Deschanel. (credit:Getty)
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Open Image ModalKate and Oliver Hudson. (credit:AP)
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Open Image ModalJulianne and Derek Hough. (credit:AP)
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Open Image ModalLauren and Breanna Conrad. (credit:Getty)
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Open Image ModalJames and Dave Franco. (credit:Getty)
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Open Image ModalChris and Scott Evans. (credit:Getty)
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Open Image ModalAnnalynne and Angel McCord. (credit:Getty)
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Open Image ModalDakota and Elle Fanning. (credit:AP)
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Open Image ModalPoppy and Cara Delevingne. (credit:Getty)
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Open Image ModalVanessa and Stella Hudgens. (credit:Getty)
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Open Image ModalBrad Pitt\'s older brother, Doug. (credit:Getty)
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Open Image ModalWhitney and Jade Port. (credit:Getty)
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Open Image ModalParis and Nicky Hilton. (credit:AP)
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Open Image ModalTaylor and Austin Swift. (credit:AP)
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Open Image ModalVictoria Beckham\'s sister, Louise Adams. (credit:Getty)
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Open Image ModalNikki and Nathan Reed. (credit:Getty)
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Open Image ModalRihanna\'s brother, Rorrey Fenty. (credit:Getty)
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Open Image ModalRyan and Mandi Gosling. (credit:Getty)
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Open Image ModalErin and Kendra Andrews. (credit:Getty)
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Open Image ModalMiley and Brandi Cyrus. (credit:Getty)
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Open Image ModalJake and Maggie Gyllenhaal. (credit:Getty Images)
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Open Image ModalRobert Pattinson\'s older sisters, Lizzy and Victoria. (credit:Getty)
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Open Image ModalJosh and Connor Hutcherson. (credit:Getty)
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Open Image ModalChord Overstreet\'s older brother, Nash. (credit:Getty)
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Open Image ModalZac Efron\'s little brother, Dylan. (credit:Pacific Coast News)
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Open Image ModalAmy, Jenny and Joanne McCarthy. (credit:Getty)
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Open Image ModalBen and Casey Affleck. (credit:AP)
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Open Image ModalJoseph Fiennes, the younger brother of Ralph Fiennes, has a twin, Jacob. (credit:Getty)
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Open Image ModalKendall and Kylie Jenner. (credit:Getty Images)
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Open Image ModalKourtney, Kim & Khloe Karashian. (credit:AP)
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Open Image ModalJessica and Ashlee Simpson. (credit:Getty Images)
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Open Image ModalAngelina Jolie and her brother James Haven. (credit:Getty Images)