Don’t let her sweet personality fool you.

Sydney Sweeney recently revealed that she is “kind of psychotic” on set and feels “bad” for her co-stars while filming certain projects.

The 27-year-old “Euphoria” star discussed her unexpected approach to acting during her appearance on “The Tonight Show Starring Jimmy Fallon” Thursday evening, where she promoted her forthcoming Apple TV+ film, “Echo Valley.”

“I, like, jump in and out,” Sweeney revealed after Fallon, 50, asked how she prepares for her roles. “It’s kind of psychotic.”

“You’re all cheerful and lively, and then…” the host remarked, prompting Sweeney to add, “And then they say, ‘Action!’ and suddenly I’m shouting and in tears. When they say, ‘Cut!’ I’m like, ‘What’s going on?’”

Set to premiere on the streaming service Friday, June 13, “Echo Valley” features the “Immaculate” actress as Claire, who is the troubled daughter of Julianne Moore’s character, Kate.

But while Sweeney praised Moore, 64, as “the most incredible human being,” she also admitted that she was “vicious” when the script called for the two actresses to argue with one another.

“She’s so kind and fun, and just amazing to work with,” the “Anyone But You” starlet said of her co-star.

“I felt so bad,” she added. “I did. ‘Cause I am. I’m vicious. I’m really vicious.”

Elsewhere during her appearance on “The Tonight Show” this week, Sweeney shared some updates regarding her “Euphoria” character, Cassie, ahead of the show’s upcoming third season.

“Cassie is crazy,” she told Fallon. “It’s the favorite version of her. She’s even worse, she’s even worse.”

Sweeney also teased the series of behind-the-scenes photos that were allegedly leaked from the set of “Euphoria” Season 3 back in April.

The pics showed the actress’ character walking down the aisle in a wedding dress, and Sweeney stayed hush-hush regarding whether the photos were real or fake.

“I can’t confirm or deny,” she said. “That could be AI!”

“No, it can’t,” Fallon fired back. “Nice try!”

One subject Sweeney did not discuss during her appearance on “The Tonight Show” on Thursday was her recent split from fiancé Jonathan Davino.

Although the pair got engaged in 2022, the “Madame Web” actress reportedly broke things off in March.

She then broke her silence on the split for the first time during an interview with The Times published on May 31.

“No,” Sweeney said when asked if she was currently planning her wedding.

“Yes,” she added when asked whether she is single.

“I’m learning a lot about myself,” Sweeney continued at the time. “Spending more time with my friends. And I’m loving it.”

The actress’ remarks came after an insider told People in March that the former couple’s relationship had been “rocky for a long time” and Sweeney “didn’t feel right” about tying the knot with the 41-year-old businessman and film producer.

“She’s exactly where she wants to be,” the source told the outlet. “Most people would feel overwhelmed by her working schedule this year, but not Syd.”

“She’s all about working right now and very excited about all her projects,” they added. “This is what she wants to focus on right now.”