Chadwick Boseman donated money from his own salary to pay Sienna Miller on '21 Bridges'

While Sienna - who has eight-year-old daughter Marlowe with former partner Tom Sturridge - had reservations about signing up for the film because she was "exhausted", she was very keen to work with Chadwick.

Sienna told Empire magazine: "He produced '21 Bridges', and had been really active in trying to get me to do it.

"He was a fan of my work, which was thrilling, because it was reciprocated from me to him, tenfold.

"So he approached me to do it, he offered me this film, and it was at a time when I really didn't want to work anymore. I'd been working non-stop and I was exhausted, but then I wanted to work with him."

The British star's fee request for the "inconvenient" movie was initially turned down by movie bosses, prompting Chadwick to step in to be paid what he felt she deserved.

She added: "I didn't know whether or not to tell this story, and I haven't yet. But I am going to tell it, because I think it's a testament to who he was.

"This was a pretty big budget film, and I know that everybody understands about the pay disparity in Hollywood, but I asked for a number that the studio wouldn't get to.

"And because I was hesitant to go back to work and my daughter was starting school and it was an inconvenient time, I said, 'I'll do it if I'm compensated in the right way.'

"And Chadwick ended up donating some of his salary to get me to the number that I had asked for. He said that that was what I deserved to be paid."

The 'Edge of Love' actress was stunned by her co-star's kindness and "respectful" behaviour and admitted she thinks it has served as a lesson to some of her male friends in the industry.

She said: "It was about the most astounding thing that I've experienced.

"That kind of thing just doesn't happen. He said, 'You're getting paid what you deserve, and what you're worth.'

"It's just unfathomable to imagine another man in that town behaving that graciously or respectfully. In the aftermath of this I've told other male actor friends of mine that story and they all go very very quiet and go home and probably have to sit and think about things for a while.

"But there was no showiness, it was, 'Of course I'll get you to that number, because that's what you should be paid.' "