NATALIE PORTMAN livid at Black Swan costar MILA KUNIS! Learn the shocking reason WHY~!

Natalie, 29, dances the lead in the ballet-themed film, but Mila’s getting Oscar buzz for her supporting role, and Natalie is NOT happy, sources say.

"This was supposed to be Natalie’s BIG role, so she’s totally upset that Mila is getting so much praise," an insider told The ENQUIRER.

"Natalie’s confident about her performance, but she clearly didn’t expect Mila to be getting so much Oscar talk."

Not unlike real life, in Black Swan, the two actresses play rival ballerinas competing for the title role in "Swan Lake."

And while Natalie was nominated for a Film Independent Spirit Award for Best Female Lead, it was Mila who was awarded the Marcello Mastroianni Award at the Venice Film Festival for best young actor.

As for the Oscars, "Natalie knows that the Best Actress category is more competitive and Supporting Actress honors usually go to an unexpected newcomer – like Mila," said the source.

"It’s like when Jennifer Hudson stole every single scene from Beyonce in Dreamgirls. And look what happened there – Jennifer walked away with the Academy Award!"