Costar: Robert and Kristen Have Incredible Chemistry

Costar: Robert and Kristen Have Incredible Chemistry
Kristen Stewart and Robert Pattinson
George Pimentel/WireImage

07/23/2009 AT 10:15 PM EDT

There is one thing about New Moon costars Robert Pattinson and Kristen Stewart that is undeniable – their attraction to one another is palpable.

"The chemistry is incredible," says costar Ashley Greene, who joined the duo at Comic-Con in San Diego to promote their new flick in the Twilight series.

Pattinson, 23, and Stewart, 19, reunited Thursday at the convention after spending most of the summer on different coasts: she in L.A. filming The Runaways (portraying rocker Joan Jett); he in New York City shooting the indie drama Remember Me.

"They're just people you can feel like you can relate to," says New Moon screenwriter Melissa Rosenberg. "That sets them apart in a lot of ways."

Rosenberg also praised the two as "genuine." The costars start filming Eclipse, the third Twilight feature, in August.

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