Dolph Lundgren threatened to knock out Sylvester Stallone while filming The Expendables

Sylvester Stallone definitely doesn't seem like the kind of person you should mess with, but Dolph Lundgren apparently ignored that instinct when he thought about 'knocking out' his Expendables co-star.

Stallone and Lundgren first appeared in the franchise together in 2010, and the success of the first film meant that their working relationship has been ongoing ever since.

With two sequels already under their belts, the pair are now returning for The Expendables 4, which is set to arrive in cinemas in September.

Lundgren spoke about the upcoming film during a recent appearance on In Depth With Graham Bensinger, where he reflected on his experiences with Stallone and admitted that the pair 'had some good times and bad times'.

He likened their relationship to being 'like family' and recalled one particular altercation which took place while the pair were filming the first instalment of the franchise.

"He was very harsh on me in a scene in Expendables 1, where he kinda yelled at me in front of the whole crew and had me do about 20 takes on a scene," Lundgren said.

"It was like, ‘My grandmother could do it better than that. What the f**k, what are you doing?’ You know, basically in front of everybody."

The actor also claimed there were 'international press' on the set that day, and when the stars took a lunch break, Lundgren was 'kind of in tears'.

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"I was really upset," he admitted, so much so that he threatened to get physical with his co-star if he said 'one more word'.

"I called my wife that time, and I basically just told her, ‘If he says one more word, I'm gonna knock him out and f**k this movie, I'm outta here. I'm just gonna punch him out and f**king leave'," he said.

Lundgren claimed that other people on the set could feel the tension between the pair, but he and Stallone soon made up.

He explained: "Then I had a tap on the back and it was Sly. And he was like, ‘Uh, I'm sorry about that. Let's just do another take and let's just keep moving on.’

"And we've had a few run-ins over the years, but what can I say, he's a crazy Italian. I think he knows that I've always respected him and loved him, and I think that's why we're still friends."

Lundgren and Stallone's relationship isn't limited to The Expendables, however, as they also collaborated on Rocky IV when Lundgren starred as Ivan Drago, who killed Rocky’s friend Apollo Creed in the ring.

UNILAD has contacted Stallone for comment.