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MARY-KATE, ELIZABETH amp ASHLEY
The Olsens were once synonymous with twosome – until kid sis Elizabeth stepped out with an Oscar-worthy performance in Martha Marcy May Marlene. "They're really important in my life," Elizabeth, 22, told USA Today of her famous older twin siblings. "I feel like they've taken care of me my whole life."
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KYLIE, KHLOé, KIM, KOURTNEY & KENDALL
It's a Kardashian world, and we're just watching it! In the last year alone, this reality TV sister act – which spans ages 14 to 32 – has conquered the world of modeling (Kendall and Kylie), motherhood (Kourtney), matrimony (Khloé and Kim)... and now divorce (Kim again). "We are obsessed with each other and would do anything for each other," big sister Kourney told Lucky magazine of their family bond.
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DEREK amp JULIANNE
It's no longer strictly ballroom for Derek and little sister Julianne. While Derek continues his run as the most winning DWTS pro (with three mirror-ball trophies), Julianne, 23, showed off her dancing and acting skills in the Footloose reboot. "Julianne is an absolute superstar," Derek, 26, told PEOPLE. "This girl is incredible. I'm so proud of her."
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WILLIAM amp HARRY
On the day he made Kate Middleton his wife, William, 29, had one constant companion at his side: his younger brother Harry, who gleefully took on the role of best man as millions tuned into the royal nuptials. "She's very lucky to find my brother," Harry, 27, said. "The two of them are a classic match."
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ELLE & DAKOTA
At 17 and 13 respectively, Dakota and Elle have spent a decade in the spotlight, even sharing a role in 2001's I Am Sam. And while the sisters share everything from a bathroom to clothes, Elle tells W of Dakota, "She is a nice older sister. But it's not like we always get along. Now that she's going to college, it's different."
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MAKSIM amp VAL
This brotherly duo turned season 13 of Dancing with the Stars into the battle of the ballroom bad boys, when the younger Chmerkovskiy joined the ABC reality competition. "We've been best friends for a long time, since birth I guess," Val, who is six years younger than Maks, told Access Hollywood. "So this whole rivalry thing is silly."
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PRINCE, BLANKET amp PARIS
In the two years since bidding farewell to their father, Michael Jackson's children have shown their resilience through grief, even taking time to enjoy life, bust a move and give back in their father's memory. "With everything I do, I try to build on what my father did," Prince Michael, 14, said. "I also try to help and change things – just like he did."