Film boss Kevin Macdonald has revealed that the Oscar-nominated actress from Carlow's real life mirrored that of her character, who falls in love with Mc Kay on screen.
How I Live Now is a dystopian tale during the outbreak of World War III, which sees Saoirse's American character, Daisy, moves to England to stay with her eccentric cousins and eventually falls in love with her relative Edmond, played by Mac Kay.
"It was Saoirse's first proper boyfriend and, in a way, I think she was living through the same thing that the character is going through.
I suspected what was going on but they kept it very quiet," he told The Independent.
"What happened during the course of film, and I'm hoping that I'm not speaking out of turn, is that they fell in love and it was very easy," he said.JJ: Did both of you pick it up at the same time or was one a better dancer than the other? SR: Yea, he did this break dance mix tape at a disco when he was like ten years old. There was a few of those things that I really wanted to steal and then just didn’t have enough time. I might find out where they are, but I want to steal it though! He was like ‘Oh yea, I won this dance competition once! The little cryopod things cause they can be used for paper weights as well. And despite the controversial subject matter of cousins falling in love, he said that he made the film with the intention of European distribution, believing it to be "too dark" for the US."I hope it's not too controversial," Mac Donald added. "The thing is, they are related by blood, but they haven't grown up together and they have never met before.Ch-ch-check out the video (above) and enjoy all the smoldering romance! It’s gonna make for one EXCELLENT romance adventure!