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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 ModalBriana and Kaley Cuoco. (credit:AP)
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Open Image ModalLady Gaga and Natali Germanotta. (credit:Getty)
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Open Image ModalSandra Vergara, Sofia's sister. (credit:Getty)
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Open Image ModalAudrina and Casey Patridge. (credit:Getty)
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Open Image ModalKate and Rooney Mara. (credit:Getty)
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Open Image ModalJennifer Lawrence with brothers Ben and Blaine. (credit:Getty)
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Open Image ModalZooey and Emily Deschanel. (credit:Getty)
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Open Image ModalLauren and Breanna Conrad. (credit:Getty)
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Open Image ModalHaylie and Hilary Duff. (credit:Getty)
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Open Image ModalJames and Dave Franco. (credit:Getty)
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Open Image ModalBeyonce and Solange Knowles. (credit:Getty)
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Open Image ModalAshlee and Jessica Simpson. (credit:Getty)
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Open Image ModalDannii and Kylie Minogue. (credit:Getty)
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Open Image ModalChris and Scott Evans. (credit:Getty)
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Open Image ModalKendall Jenner, Khloe Kardashian, Kourtney Kardashian and Kylie Jenner. (credit:Getty)
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Open Image ModalSienna and Savannah Miller. (credit:Getty)
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Open Image ModalRafaela, Gisele and Patricia Bundchen. (credit:Getty)
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Open Image ModalJulianne and Derek Hough. (credit:AP)
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Open Image ModalKate and Oliver Hudson. (credit:AP)
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Open Image ModalAnnalynne and Angel McCord. (credit:Getty)
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Open Image ModalEmma and Alex Watson. (credit:AP)
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Open Image ModalPoppy and Cara Delevingne. (credit:Getty)
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Open Image ModalJustin and Sebastian Theroux. (credit:FameFlynet)
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Open Image ModalVanessa and Stella Hudgens. (credit:Getty)
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Open Image ModalWhitney and Jade Port. (credit:Getty)
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Open Image ModalChris and Liam Hemsworth. (credit:AP)
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Open Image ModalElizabeth Olsen is the younger sister of Mary-Kate and Ashley Olsen. (credit:Getty)
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Open Image ModalScarlett Johansson and twin brother, Hunter. (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 ModalDakota and Elle Fanning. (credit:Getty)
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Open Image ModalAndrew, Owen and Luke Wilson. (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 ModalMiley and Brandi Cyrus. (credit:Getty)
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Open Image ModalRyan and Mandi Gosling. (credit:Getty)
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Open Image ModalZac Efron's little brother, Dylan. (credit:Pacific Coast News)
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Open Image ModalBlake Lively's older brother, Eric. (credit:Getty)
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Open Image ModalErin and Kendra Andrews. (credit:Getty)
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Open Image ModalJake and Maggie Gyllenhaal. (credit:Getty Images)
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Open Image ModalBrad Pitt's older brother, Doug. (credit:Getty)
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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 ModalAmy, Jenny and Joanne McCarthy. (credit:Getty)
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Open Image ModalMichelle Pfeiffer's younger sister, Dedee. (credit:Getty)
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Open Image ModalBen and Casey Affleck. (credit:AP)