The 47-year-old singer-turned-actress had to "strip down" her look for her role as downtrodden Florence in Dee Rees' new movie and was amazed at the number of compliments she received.
She said: "I'm used to my nails now, and I'm addicted to lashes.
"I'm Mary J. Blige. I mean, like, this is what I do. I wear wigs, I wear bob wigs, and I had to completely strip down to my own natural hair texture, which I've always been afraid of.
"Dee stripped me down all the way to what I truly am, and people were complimenting me. People were saying how beautiful I was. I didn't know I was that beautiful for real. You understand what I'm saying? I didn't know that."
The 'Family Affair' hitmaker admitted her friends were surprised by how "great" she is in 'Mudbound' - and she was equally shocked.
She told New York magazine: "Everyone I see, they say, 'Oh, my God, you were so great. I didn't know.' They didn't know I had whatever they're seeing in me; they didn't know I could pull it off. To be quite honest, I didn't even know I did that good."
And playing Florence taught the star that she is more "powerful" than she knew.
She said: "I learned that I'm a really powerful woman. I mean, other than just being Mary J. Blige, the superstar, I learned that I'm powerful because I don't have to say much to be heard."
While shooting 'Mudbound', Mary was on the verge of filing from her husband and manager, Martin 'Kendu' Isaacs but didn't tell anyone on the set.
She said: "It wasn't anybody's business. I just kept it and gave it all to Florence...
"I hate pain, but I know how to deal with it
"To do the assignment God has sent me to do, I have to live certain things. And unfortunately I'm constantly living it. You understand what I'm saying? It's like trying to talk to a prison class, but you've never been to prison."