Luke Evans had to go easy on Emily Blunt when the pair filmed a fight scene for 'The Girl on the Train' because she was four months pregnant.

As they were about to shoot the intense scene which involved a scuffle, Blunt whispered to her co-star that she was expecting her second child with husband John Krasinski to ensure he wasn't too rough with her.

Evans believes other than the 33-year-old actress' family he was one of the first people to know about the pregnancy.

In an interview on UK TV show 'This Morning', he recalled: "In this scene there was a kerfuffle and just before we were about to do it, she leaned in and whispers, 'I'm four months pregnant.' I was like, 'What?' She said, 'I'm four months pregnant.' She decided to tell me at that moment so I think I was one of the first ones to find out. But she had to tell me, I was about to throw her around the room, I was like, 'Cheers Em!' But she was a pro and didn't let it affect her."

Blunt went on to give birth to daughter Violet in July, a younger sister for two-year-old Hazel.

Hawkins' book was set in London but the movie sees the plot re-located to New York City.

For his role Welshman Evans had to deliver his lines in an American accent and he was confused when his fellow Brit Blunt spoke her dialogue in her normal voice.

He said: "No one had told me until our first take and I was like, 'What's going on?' Her accent is terrible! It really threw me off on a tangent."

Evans attended the world premiere of 'The Girl on the Train' in London with Blunt on Tuesday night.

The pair were joined on the special 'red carpet' which was made to look like a train track by their co-stars Rebecca Ferguson and Haley Bennett and director Tate Taylor.