Justin Theroux Is "Icy" And "Fishy," Jokes Girlfriend Jennifer Aniston

What's Justin Theroux really like?

"He's just the most cold, icy, fishy kind of a guy," his girlfriend Jennifer Aniston joked on Good Morning America Monday. "I'm trying to warm him up, but you know..."

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All kidding aside, Aniston, 43, said her beau of less than a year "is really cute" and "a great actor." (The two became an item while shooting Wanderlust, in theaters February 24.)

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Aniston added that she's "known Justin for a long time. We met when he was shooting Tropic Thunder."

Shooting Wanderlust in a remote location with Theroux, 40, Paul Rudd, 42, and Malin Akerman, 33, was a dream come true for Aniston.

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"The main thing that was so refreshing for me was being in Clarksville, Georgia, which was so far in the middle of nowhere. There's sort of a parallel experience happened between what happened with my character in the movie and with me in life," Aniston said. "All of my guards fell away. I felt this weight off of my shoulders of constantly being on guard or looking over my shoulder or [asking], 'What's that over there?' or 'Who has a cell phone?'"