Mavis! details the star's rise to fame as a member of her family group the Staple Singers and her campaign work during the Civil Rights Movement in the 1950s and '60s, during which she marched alongside Dr. Martin Luther King, Jr. to demand equal rights for African-Americans.

Staples, 75, worked closely with director Jessica Edwards on the movie, but she admits delving back into her past proved painful at times and she almost pulled out of the project.

She tells People.com, "It was hard. All the memories came back. I just couldn't help but cry. I'd have to tell them (filmmakers) to wait on me, to just excuse me for a minute. I just blubber when I see certain parts of it. And I told my manager at first, 'I'm tired of talking about 'Back when,' I don't wanna do this.'

"But he said, 'You've lived through so much, you should talk about (it).' So I thought, maybe it should be documented, what we went through, what all happened, while I'm still here to tell it. It brought back a lot of terrible feelings... and some happy ones, too."

Mavis! received its world premiere at the South by Southwest film festival in Austin, Texas in March (15) and is due to air on America's HBO cable network later this year (15).