01/08/2013 08:19 am ET

Justin Bartha Is Dating Trainer Lia Smith (PHOTO)

Justin Bartha's "mystery woman" is in fact his girlfriend, trainer Lia Smith, a source reveals to PEOPLE.

The pair recently enjoyed a cozy trip to Smith's native Hawaii and were snapped basking in the sun on Maui on New Year's Day, which got people buzzing about her identity.

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