Brie Larson: 5 things to know about 'Captain Marvel'

For the first time, Captain Marvel will appear on screen in a Marvel Universe film. Brie Larson, who stars in the role, stopped by the ABC News studios to talk about taking on one of the most buzzed about characters in superhero history.

1. Larson kept a big secret about "Captain Marvel" for at least a year

When Larson snagged the coveted role of Carol Danvers aka Captain Marvel, she didn’t even tell her mom about it!

“It was three years ago that I found [out]. And I couldn’t tell anybody for a year,” Larson said in an appearance on “Popcorn with Peter Travers.” “I didn’t tell anybody. Now looking back on it, I’m like, Marvel would have understood if I told my mom. But I just didn’t tell anyone because it was too hard. And like, it was hard for me to keep the secret. And I didn’t want anybody else to feel how I was feeling when it came to keeping the secret.”

2. “Captain Marvel” is Larson’s third movie with Samuel Jackson

Larson and co-star Samuel Jackson have teamed up for several films and enjoy working together.

“This is my third film with him. And we’re trying to scheme up what the next three will be,” Larson said. “He’s just like one of my favorite people on the planet. He’s my family at this point. And it’s interesting because he’s been there. And now, kind of reflecting and doing a little supercut of my life, he was there with me on ‘Kong’ when I was dealing with the awards season hullabaloo. And then he was there when I directed my first feature. And now he’s in this with me. So all of the big moments in my career, he’s been there for.”

3. Larson is severely allergic to cats

Larson’s cat allergy is a bit of a bummer because one of her co-stars in the “Captain Marvel” film is a scene-stealing cat. She said there was no way to prepare for him.

“If I could have spent 9-months prepping for cats, maybe I should have done that, just like slowly expose myself to more cats so that I was more ready,” she said. “Those were tougher days for me. I swell up. I can’t breathe. It’s bad. I’ve been allergy tested and the doctor was like, ‘oh, that’s the worst I’ve ever seen for cats. It’s pretty bad’.”

4. Larson has not signed on for 7 more "Captain Marvel" movies

Despite rumors, Larson said she has not signed on for seven more Marvel movies.

“I’m not going to talk about my contract,” Larson, 29, told Travers. “But I will say that whatever the rumor is that I’ve signed on for seven is not true. That would be a very long time.”

5. Larson trained for 9 months for her "Captain Marvel" role

Larson wanted to ensure that she’d done everything possible to prepare for her debut as Captain Marvel. She spent more than half a year training for the role.

“I trained for nine months, which was my choice, no one said you have to,” said Larson. “I like a 9-month prep. That’s like my ideal. Because I feel like it gives you time to completely change. Like you can really change your mind and think in a different way after 9-months. It gives you time to find it and lose it again and find it. And that’s what happened with this. So I had about 6-months of cardio and strength training. And then three months before we started shooting I added in fight training as well.”

"Captain Marvel" hits theaters everywhere today.

Walt Disney is the parent company of ABC News.