Cast member Portman poses at the premiere for "Annihilation" in Los Angeles. Picture: Reuters

Acclaimed actress Natalie Portman could make a surprise appearance in the fourth 'Avengers' movie.

The Academy Award-winning actress played the part of Jane Foster in the 'Thor' franchise, and director Anthony Russo - who is helming the project alongside his brother Joe - has hinted at Natalie returning to the Marvel Cinematic Universe.

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Asked whether the character of Jane was still alive, Anthony and his brother became coy and refused to commit to an answer because it might've given fans an insight into their plans.

He told HuffPost: "When we say spoiler, [we mean] potential spoiler."

Jane last appeared in a Marvel movie in 2013's 'Thor: The Dark World', but Natalie has previously admitted to being open to a return to the franchise.

The 36-year-old actress shared: "It is really an incredible thing to get to be part of. As an actor it is like a completely different scale.

"Because when you are making those movies, you are working with so much blue screen and so much fantasy. Your imagination has to be so much larger."

By contrast, Natalie said in 2016 that she was "done" with Marvel films.

She explained: "As far as I know, I'm done. I don't know if, maybe one day, they'll ask for an 'Avengers 7' or whatever. I have no idea! But as far as I know I'm done. But it was a great thing to be a part of."