Lily Gladstone Reveals the Scene Partners That ‘Terrified’ Her More Than Leonardo DiCaprio and Robert De Niro (Exclusive)

After starring in Killers of the Flower Moon alongside the likes of Leonardo DiCaprio and Robert De Niro, one might think few actors could rattle Oscar nominee Lily Gladstone. But then she met her Under the Bridge costars.

In the Hulu limited series based on the true story of the 1997 murder of teen Reena Virk by her classmates, Gladstone plays cop Cam Bentland, a composite character representing the local police working on the case. While she frequently shares the screen with costar Riley Keough, who plays journalist Rebecca Godfrey (who wrote one of the books upon which the series is based), many of her scenes are with the young actors playing the teens in Reena's circle: Chloe Guidry, Izzy G., Aiyana Goodfellow and Javon "Wanna" Walton.

"Each one of those kids, when I was blessed enough to be in the scenes with them, they upped my performance," Gladstone, 37, tells PEOPLE. "Walking out of working with Leonardo DiCaprio and Robert De Niro, the scene partners that have terrified me the most in the last couple of years have been these kids because they're so good. They don't lie."

"And you can tell these kids — who are all actors and want to be actors and have been studying it — they've grown up watching some really incredible performances," she continues. "There's way more complex characters for their age group, and they handle it so beautifully. The strength of all of their performances and what they brought to their roles is just so indicative of how much kids are capable of. They live and breathe what they do."

Adds Keough, 34: "I had moments with every single one of them that I was blown away by. There's a rawness or an honesty in younger performers, I think, that's really powerful when you're working with them."

Those intense and impressive performances by the show's rising stars were essential to the series because, as Gladstone says, "The whole story revolves around the power of the teenage girl."

Off-screen, Gladstone says, the young actors became great friends.

"That was an interesting balance, to see these beautiful kids who are so supportive of each other, who are just such good friends with each other, who miss each other when one is has a day and the other one's gone home for the weekend," Gladstone recalls. "Chloe and Vritika [Gupta, who played Reena] are very close. Chloe was always sending little videos to her when she wasn't there and felt almost protective of her, I think, because Vritika was the youngest out of all of the kids."

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A similar support system existed between Gladstone and Keough as well, who first connected via social media in 2018 and were excited to work together on Under the Bridge.

"Lily's the kindest, most gentle, sweetest soul, so she's very easy to work with when you have scenes that are heavy," Keough says. "And I just love watching actors so much, and it's just such a joy, and when you're a fan of someone and then you get to work with them and watch them perform, it's just like.... Even if the material is heavy, it's such a beautiful thing to experience it when you perform with someone that you're a fan of."

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New episodes of Under the Bridge drop Wednesdays on Hulu.