The Wrestler star has become close friends with the gay sportsman through working together on the currently untitled film, which will document Thomas' career and his place in history as the first high-profile rugby player to 'come out' as homosexual.
Thomas has now revealed he took Rourke on an unusual night out in London to give him an insight into the city's gay scene.
He tells Britain's Daily Star on Sunday newspaper, "When he was in London, I took him to some gay bars in Soho. We planned to go gay clubbing but we didn't want to get pictured going out. We just wanted to go out and have fun and let him experience a gay club."