(CNN) Fans are crossing their fingers that Dr. Jane Foster is returning to save the world once again.

Natalie Portman, who played the beloved scientist and love interest in the first two "Thor" films, appeared at the "Avengers: Endgame" premiere Monday in Los Angeles.

Her unexpected presence has prompted people to speculate that Foster is returning in the fourth and final installment of the Avengers franchise.

Natalie Portman's at the premier...I'm sure this is a reach but....is it possible that Jane Foster might be in the movie?!?! — Allannia 🌻 (@allanniaveliz) April 23, 2019

natalie portman to suddenly show up at the endgame premiere can only mean one thing.......jane foster thor is about to beat yall asses — alia 🦇 | endgame TODAY (@Iokified) April 23, 2019

Some fans even hypothesized that the the brilliant astrophysicist will be the key to defeating Thanos, the purple supervillain who wiped out half the universe's population in "Avengers: Infinity War."

JANE FOSTER WILL DEFEAT THANOS #NATALIEPORTMAN pic.twitter.com/GEU9WGYFpd — səb | was cheridcn (@damerogcrs) April 23, 2019

Foster appeared in 2011's "Thor" and 2013's "Thor: The Dark World," but Portman's character did not return for "Thor: Ragnarok" in 2017. Foster's name was mentioned in passing by Thor in subsequent Marvel movies, but it's presumed that the two broke up.

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