EXCLUSIVE: Alicia Silverstone Reveals Her Biggest 'Clueless' Regret and the Real Life Mean Girl Who Inspired C

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Oh my gosh -- we're totally buggin'!

Alicia Silverstone surprised fans at a Cinespia's Clueless screening in the Hollywood Forever Cemetery in Los Angeles on Sunday -- and only ET caught up with the 40-year-old actress to celebrate the film's success and uncover some exclusive behind-the-scenes secrets.

Silverstone, who brought her six-year-old son Bear Jarecki to the Clueless screening, confessed that this is the first time that her little look-alike will be seeing his mom in the film. "He might get bored but whatever we'll see," she said with a laugh. "I said it's girls talking about boys and clothes and things, and he was like 'That sounds cool!'"

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PHOTOS: This Is What the 'Clueless' Cast Looks Like 20 Years Later

It's been 22 years since Clueless introduced the world to key phrases like, "whatever" and "as if," and Silverstone admitted that when she first stepped into Cher's now-iconic heels, she had "no idea" that the film would become the beloved cult classic that it is today.

"I remember driving back from doing one of the Aerosmith music videos, because it was now the third one [I had done] or something," she recalled. "I was in Santa Barbara and I was reading [the Clueless script] in the back of a car and I remember thinking, 'This is so funny, but I'm not funny! I don't know how I can do this.'"

As we all know, she certainly did -- and only ET knows how!

MORE: ‘Clueless’ 20 Years Later: What Alicia Silverstone and Paul Rudd Think About the Film

Back when Clueless was being filmed in 1994, ET was on set with 18-year-old Silverstone, and the fresh-faced actress dished to our cameras about the real-life inspiration she used to get into character.

"When I grew up I did not like these kinds of girls," young Silverstone said of Cher Horowitz and her Beverly Hills posse. "I could not stand them, so it was hard for me to even, like, get into this character because that was something I've always hated."

"I grew up in a nice area and all these girls had everything and I knew all these kinds of girls -- one in particular," she continued. "But they one thing they don't have, which Cher does, is that solid, 100 percent, pure good heart and happiness."

When we asked Silverstone about that "one in particular" mean girl, the blonde beauty burst into giggles. "I think I know who I was talking about, but we're really good friends now so it's really funny!" she exclaimed.

RELATED: 'Clueless' Fashion Still Has Us Buggin' 20 Years Later

While Cher may have been the main character in Clueless, Silverstone admits that the brightest star will always be the film's fashion. "Mona May the [Clueless costume] designer was so brilliant, and I remember a funny story which is at that time in my life, I wore jeans and a green t-shirt every single day and that was it," she said.

"I just didn't get fashion at all," Silverstone added. "I was just kind of a tomboy and I just wasn't into it, so when we had the [Clueless] fittings, I was just like, 'What is going on? Why am I in these fittings for so long?' I just didn't get it until I saw the movie and I was just like, 'Oh I get it! The costumes are the star of the movie!'"

Shortly after her time on Clueless, Silverstone revealed that she suffered a major fashion faux pas that she still regrets.

"I took so much of the clothes and I'm really sad because I don't have any of them anymore because, like a ding dong, I got home with so many of the clothes and I was like, 'How am I going to wear these Mary Janes out now?' she explained. "Like, that girl who wore jeans and a green t-shirt didn't know how to transition and of that wardrobe, so I just gave a lot of it away. I don't have any of it but I had a lot of it."

WATCH: Behind the Scenes of 'Clueless' and the Never-Before-Seen Cast Photos

Do you hear that? That's the sound of millions of 90s girls collectively screaming in horror…

Press play on our exclusive flashback video below to see more on-set footage from Clueless and see the cast partying it up at their premiere beach bash!