Gerard Butler almost killed Hilary Swank in freak accident while filming P.S. I Love You

The plot of P.S. I Love You had audiences in floods of tears when it dropped all those years ago, but people were nearly left crying for a far darker reason.

And that's because one of the romance-drama's main stars Gerard Butler nearly killed his on-screen widower Hilary Swank in a freak accident.

Thankfully she lived to tell the tale, although she didn't come out of it completely unscathed.

The Olympus Has Fallen star took to a recent episode of The Drew Barrymore Show where he opened up on a variety of topics, including the time he sent Swank to the hospital.

It came about when Barrymore invited Butler to take part in her game 'Behind the Scenes' which involves guests being shown scenes from their movies and sharing the first thought, anecdote or 'naughty detail' that comes to their head.

The final snapshot is one from P.S. I Love You, a film about Holly (Swank) and her husband Gerry (Butler) who are tragically torn apart when the latter dies.

As Holly grieves, she discovers Gerry has left behind 10 letters, each signed with ‘P.S. I love you,’ designed to help Holly overcome her grief and move on with her life.

When the scene came up in Barrymore's show, Butler launched into the story, starting off by explaining that when he took on the role, rather than thinking about himself, he decided to only focus on Swank and how she was doing – as that's exactly what his character did with his wife.

"It made the experience so much more fun when I got out of my own head," he says before joking, "She's so cool and great to work with that I almost killed her."

YouTube/The Drew Barrymore Show

Butler continues: "You know the scene where I’m dancing and I have the, what do you call them, suspenders?

"I literally shot that scene for a day and a half, and I had to dance like an idiot in the suspenders.

"It was like that first moment in 300, you're like, 'I can't believe I'm doing this dance in my boxer shorts'.

"And then at one point, the clip, which was a crocodile clip, got stuck in the television as I’m crawling towards her, and she’s right in front of me and she's laughing hysterically.

"The camera people had these plastic fronts to protect themselves from this crocodile [clip] – it was so dangerous – because I had to ping it, and it would go past my face.

"And this time I’m crawling towards the bed, it gets stuck, it releases, flies over my head, hits her in the head, slashes her head.

Warner Bros.

"I cut her – you could even see the teeth [marks of the clip] and she had to get taken to hospital."

Unfortunately, the awkwardness didn't end there. As everyone in the studio rushed Swank away, Butler was left sat there in his boxer shorts all on his lonesome.

"I just started crying," he adds, saying that he felt the full force of 'imposter syndrome' after accidentally injuring his co-star.

Bless him. Thankfully he didn't kill anyone and the movie went on to be a great success, earning a respectable 80 percent audience score on Rotten Tomatoes.