The Twilight star opens up on filming alongside his girlfriend

Twilight star Robert Pattinson‘s steamy sex scenes with Kristen Stewart in Breaking Dawn have left him wondering how on earth the film will be put on general release for a teenage audience.

‘The main story line is…so far outside of the box,’ says Robert, 24.

‘It’s really different from the other ones.

‘There are some days on set just watching [when] you go, “How is this going to be PG-13?” It’s like totally ridiculous.’

The star, who plays Edward Cullen in the popular vampire saga, reveals little about the upcoming film – but he does admit he thinks real-life girlfriend Kristen, 20, is well suited to her vampire alter-ego.

‘I can’t give too much away but there’s some bits, especially towards the end of the movie, she’s just like the polar opposite of any of the other films,’ he tells USA Today.

‘I mean, she’s a different person, which is cool. She looks completely different.

‘She looks probably the most convincing vampire out of all of us.

‘A lot of us look like we’re just from Mars.

‘She’s kind of the smallest one, but she suits being a vampire.’

Robert Pattinson and Kristen Stewart | Robert Pattinson and Kristen Stewart film Twilight Saga: Breaking Dawn | Now Magazine | Pictures

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Esme Riley