Madelyn Cline on Her 'Glass Onion' Role and Getting in Trouble for Spilling 'Outer Banks' Secrets (Exclusive)

'I'm bad with secrets!'

Glass Onion star Madelyn Cline did a good job not spilling any secrets about the new Knives Out film when she sat down with ET's Ash Crossan recently -- but she hasn't always been so lucky!

The actress and co-star Jessica Henwick were sharing a laugh about which of their A-list co-stars in Rian Johnson's new murder mystery would be the best help at hiding a body, when Cline let it slip that she would be worried about her ability to keep the hypothetical crime under wraps.

"I'm bad with secrets," she admitted, explaining that she once got in trouble with a confidentiality leak on her Netflix drama, Outer Banks. "I accidentally spoiled the release date."  

"It's funny, since then, now all my emails with information not to be shared until a certain date have like, even bigger, bold red letters that say 'CONFIDENTIAL,'" she added.

Outer Banks season 3 is set to premiere next year -- and recently shared the first trailer from the new episodes -- but in the meantime, Cline has her role in Glass Onion, which she told ET is "very exciting."

In the mystery film -- which finds Daniel Craig's Knives Out detective, Benoit Blanc, tracking another murder case, this time in Greece -- Cline plays Whiskey, an online influencer and girlfriend to Dave Bautista's Duke, a famous Twitch streamer.

"I just opened up Instagram and YouTube and went to town," the actress said of preparing for the role. "I feel like Whiskey is kind of a mish-mash of people that I have seen, met and had the joy of watching be the characters that they are, especially here in L.A. So that was really fun."

As for Henwick, she said that her "strongest" memories from making Glass Onion were hanging out with Cline and their castmates outside of work, noting that even though "the whole thing was a vacation," they did get into "some life-or-death situations."

"I'm just saying that Greece needs street lights for their roads, 'cause they're very curvy and they go into the mountains," she added with a laugh. "Also, ATVs. They need mirrors on the turns around the mountains. It's just a very dangerous place."

Glass Onion: A Knives Out Mystery will have a limited theatrical release starting Nov. 23 before streaming on Netflix on Dec. 23.