The director of the first "Twilight" movie revealed she was nervous about having Robert Pattinson kiss co-star Kristen Stewart when she was underage. 

The first movie came out in 2008 after the books by author Stephanie Meyer became a cultural phenomenon. As part of the audition process, the two leads of the franchise met at director Catherine Hardwicke’s home where they did a screen test together that included a kissing scene, which gave the director some serious second thoughts after it happened. 

Speaking on "The Big Hit Show" podcast recently, Harwicke explained that she had the duo over to her home in 2007 and brought them to the bedroom where they allegedly went a little overboard while testing their chemistry during a scene that required the characters to kiss. The director revealed that Pattinson fell off the bed at one point because they got so into it. 

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Kristen Stewart and Robert Pattinson did a screen test for "Twilight" when she was underage. (Jon Kopaloff/FilmMagic)

"Rob and Kristen auditioned on my bed, the kissing scene, Rob was so into it he fell off the bed. I’m like, ‘Dude, calm down.’ And I’m in there filming with my little video camera, whatever," she recalled while giving the podcast a tour of her home (via The New York Post). 

After the scene was done, they realized that it was a good fit. Hardwicke recalls Stewart telling her "it has to be Rob." However, that’s when something dawned on her. At the time the actress was 17 and Pattinson was 21. 

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The director of Twilight revealed the two leads kissed in their screen test. (Elisabetta A. Villa/WireImage)

"I could tell they had a lot of chemistry, and I’m like, ‘Oh my God.’ I thought, Kristen was 17. I don’t want to get in some illegal things," she said. 

The director added: "So I remember I told Rob, ‘By the way, Kristen is 17. In our country, it’s illegal to have a sexual … ‘ And he’s like, ‘Oh, OK, whatever,'" she added.

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It’s not surprising that the two actors had chemistry together upon first meeting each other given that they went on to date in real life for nearly four years before ultimately calling it quits amid rumors of infidelity, according to Us Weekly.

Kristen Stewart and Robert Pattinson kissed during their "Twilight" screen test. (Chris Polk/FilmMagic)

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However, it seems that the minds behind the movie ended up being fine with the age difference between the stars and they went on to make not only the first film but four more after that including "The Twilight Saga: New Moon," "The Twilight Saga: Eclipse" and "The Twilight Saga: Breaking Dawn - Parts 1 and 2."