Justin Timberlake `hoped to fall in love with Amanda Seyfried`

The 30-year-old actor said that his co-star is so 'beautiful' that he wanted to fall head over heels for her whilst making the futuristic action film.

'I have a clause in my contract that says if you put someone as beautiful as Amanda in the movie, I have to fall in love with her,' he told People magazine at the San Diego Comic-Con.

But Seyfried said that there relationship extended solely to going shooting after work.

'There are a lot of guns, which we both really enjoyed,' she said. 'We sometimes went shooting after hours.'

And Timberlake, who split with girlfriend Jessica Biel earlier this year, also got close to actress Olivia Wilde, who plays his mother in the movie.

'It was a mind trip for me,' he admitted about having a 27-year-old play his mum. 'Olivia is two or three years younger than me, so to have her playing my mother was definitely a head trip.'

'I'd just like to point out that [my song] Mother Lover is about sexing up someone else's mother,' he added.