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Does Mary-Kate Olsen have a new man?

A source tells the 24-year-old has taken her relationship with Seth Campbell public, partying with the "chill" shoe designer at multiple New York City hotspots.

"Their relationship is fairly new," a source tells Us of the duo, who celebrated a mutual friend's birthday Feb. 16 at NYC's Lavo. "They've been able to have a few dates on the down low. He's a downtown kind of guy, likes to party every now and then."

When reached for comment, a rep for the actress tells Us it is "not true" that Olsen and Campbell are dating.

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Olsen split from artist Nate Lowman in February 2010 after two years together.