Portman -- along with her Lucy in the Sky co-star Jon Hamm -- sat down with ET's Ash Crossan at a junket for their upcoming drama, and she opened up about her recent appearance at this year's San Diego Comic-Con, and her return to the Marvel Cinematic Universe.
When asked about what lead to her decision to reprise her character, scientist Jane Foster, Portman explained, "They came to me with the idea and said, 'We have this idea for you that was a storyline in some of the comics where Jane becomes Lady Thor,' and I was like, 'This is very exciting!'
Regarding her temporary departure from the series, Portman said, "Obviously, I wasn't written into [Thor: Ragnarok] because of where it took place. It wasn't really on Earth, and my character is on Earth."
Ragnarok -- the third film in Thor's standalone series within the MCU -- largely took place on the violent, distant planet of Sakaar, and Thor's homeworld of Asgard. It was the first Thor film to be helmed by director Taika Waititi, who has also been tasked with overseeing the upcoming Love and Thunder.
The film will see Jane Foster take on the powers of Thor, and to announce the casting, Portman appeared during the Marvel panel at SDCC in July, where she held Thor's mighty hammer in the air to the delight of the fans.
Portman told ET she's looking forward to working with Waititi and "I love Tessa [Thompson] and Chris [Hemsworth] so much, so it's exciting to work with them again."
"And I'm very excited to wield the hammer," she added with a smile.
As for her upcoming performance in Lucy in the Sky -- in which she plays an astronaut who returns home from a long trip into space, sparks a romance with a fellow astronaut, and begins to lose touch with reality and her sanity -- Portman explained how it felt to work with Reese Witherspoon, who produced and shepherded the project.
"Reese was very involved, she helped develop the script so I am very grateful to her for helping create this character and working on details of it with [director] Noah [Hawley] during the development… it was so lucky," Portman said of Witherspoon, who was originally slated to star in the project before she decided to step back behind the scenes and hand the reins over.
"She's such a powerhouse," Portman added. "She's producing and making work for a lot of us, so I'm very grateful and it was really lucky to get to have a friend to get to call up and be like, 'What do you think about this? What's your take on this? Why did you choose this?' It was very lucky to have her insight."
Lucy in the Sky rockets into theaters Oct. 4. Thor: Love and Thunder is slated for release in November 2021.