Boseman, who died aged 43 after a four-year battle with colon cancer, was one of the producers of the film, and was therefore instrumental in getting Miller to take part in the production.
However, with the 38-year-old Layer Cake actor wary about taking the role, and the studio unwilling to meet her wage demands, Boseman stepped in and offered up some of his salary to take the amount up to the requested number.
Speaking to Empire, Miller explained: "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."
She continued: "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.'
"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."
Miller added: "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.'"
Sadly, Boseman lost his battle with cancer on 28 August this year, but since his death people have been queuing up to talk about his generosity and kindness.
His Black Panther co-star Michael B Jordan said: "One of the last times we spoke, you said we were forever linked, and now the truth of that means more to me than ever,
"Since nearly the beginning of my career, starting with All My Children when I was 16 years old you paved the way for me. You showed me how to be better, honour purpose, and create legacy. And whether you've known it or not... I've been watching, learning and constantly motivated by your greatness.
"You cared about me. You are my big brother, but I never fully got a chance to tell you, or to truly give you your flowers while you were here. I wish we had more time,
"I'm dedicating the rest of my days to live the way you did. With grace, courage, and no regrets. 'Is this your king!?' Yes . he . is! Rest In Power Brother."
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