Sienna Miller says Chadwick Boseman donated part of his salary to her

Actor Chadwick Boseman died of cancer on August 28 aged 43. Photo / AP

Sienna Miller has opened up about Chadwick Boseman's "astounding" act to ensure the British actress was paid what she was worth.

The Black Panther actor, who lost his battle with colon cancer last month aged 43, starred alongside Miller, 38, in the 2019 thriller 21 Bridges, which is currently streaming on Neon in New Zealand.

And for the first time, Miller has revealed in an interview with Empire she almost wasn't going to sign on to star or co-produce as the studio wouldn't agree to her asking price.

She said it was an "inconvenient time" as her daughter was just starting school.

"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," Miller said.

"He said that that was what I deserved to be paid.

"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."

Chadwick Boseman and Sienna Miller starred in 21 Bridges together. Photo / Getty Images

Miller said the selfless act was "unfathomable" in the entertainment industry, which is notorious for gender pay disparities.

"It was about the most astounding thing that I've experienced," Miller said.

"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.'"

Only a handful of people outside of Boseman's family had knowledge of his cancer diagnosis, including his producing partner Logan Coles, his agent, his trainer and Brian Helgeland, the director of the star's breakout film 42.

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It is with immeasurable grief that we confirm the passing of Chadwick Boseman.⁣ ⁣ Chadwick was diagnosed with stage III colon cancer in 2016, and battled with it these last 4 years as it progressed to stage IV. ⁣ ⁣ A true fighter, Chadwick persevered through it all, and brought you many of the films you have come to love so much. From Marshall to Da 5 Bloods, August Wilson’s Ma Rainey’s Black Bottom and several more, all were filmed during and between countless surgeries and chemotherapy. ⁣ ⁣ It was the honor of his career to bring King T’Challa to life in Black Panther. ⁣ ⁣ He died in his home, with his wife and family by his side. ⁣ ⁣ The family thanks you for your love and prayers, and asks that you continue to respect their privacy during this difficult time. ⁣ ⁣ Photo Credit: @samjonespictures

A post shared by Chadwick Boseman (@chadwickboseman) on Aug 28, 2020 at 7:11pm PDT

Boseman chose to keep his cancer battle private from the Marvel team.

Disney, which has made no announcement regarding plans for Black Panther II and any planned appearances for Boseman's King T'Challa, is said to be focusing on paying tribute to the late star rather than developing plans.

Posthumously, he will appear in Ma Rainey's Black Bottom alongside Viola Davis.