NEW YORK – “This isn’t your mother’s ‘Mean Girls.’ ”

It’s the tagline that launched a thousand existential crises among millennials last fall when the first trailer premiered for the “Mean Girls” movie musical (in theaters Friday). The new film is adapted from the 2004 high-school comedy and 2018 Broadway show, all written by “30 Rock” mastermind Tina Fey.

“That was the Paramount marketing department and then the millennials were so butthurt,” Fey says with a laugh, seated at a hotel overlooking Central Park. “It was like, yes, you guys are getting old! It did expose a little millennial narcissism: When you went, there were other people in the theater too! And some of them may have been older than you! It was so centering themselves in the story.”

Tina Fey thanks cable TV for 'Mean Girls' phenomenon

Based on Rosalind Wiseman's 2002 book "Queen Bees and Wannabes," the original "Mean Girls" followed naïve new kid Cady Heron (Lindsay Lohan), who's recruited into taking down popular girl Regina George (Rachel McAdams) and winds up becoming her mirror image. The movie was an instant sensation, bringing "fetch," "grool" and "Glen Coco" into the lexicon, along with dozens of other phrases that are now millennial parlance ("Boo, you whore").

It was when "Mean Girls" opened on Broadway, earning 12 Tony Award nominations, that Fey realized it had crossed over to the next generation.

"People were coming with their kids; people were coming with bachelorette parties," Fey, 53, recalls. "Because (the movie) was always on TBS, it felt like it was a net that would just catch people as they turned 11, 12, or 13. I guess we have cable TV to thank, really."

The movie's young stars can't remember life without "Mean Girls": Pop singer Reneé Rapp, who plays Regina, was only 4 years old when she first saw the PG-13 comedy. (She even has a "sick" photo to prove it.) Australian actress Angourie Rice, who portrays Cady, similarly watched the movie "over and over again" as a little girl.

"My mum was like, 'This has a good message,' " Rice, 23, says. " 'This is about young women figuring out their lives, it's not putting them down, and in the end, they're all OK.' "

The 'Mean Girls' movie musical aims to be 'timeless,' not 'trendy'

The new "Mean Girls," directed by Samantha Jayne and Arturo Perez Jr., is modernized in key ways. The musical's songs are revamped with TikTok-friendly arrangements, and parts of the story are now told through smartphones and social media posts. But the film doesn't rely on Gen Z lingo or references ‒ some of the best new jokes are about "iCarly" and teachers unions. Plot devices from the original movie, such as Kälteen Bars and the Burn Book, are also left unchanged.

"I do sometimes run things by my kids," says Fey, whose daughters Alice and Penelope are 18 and 12, respectively. "Early on, there was conversation of, 'Would the Burn Book still be a physical book or should it be a private Instagram?' I knew what my instinct was, but I ran it by my kids. And my older daughter was like, 'Yeah, no. Don't let those millennials overthink it!' "

"She's correct," Rice adds. "It all still felt timeless. Nothing felt like, 'Oh, we're doing this because it's trendy.' "

Fey also looked to the 1978 movie musical "Grease" in her judicious approach to cutting songs. (Her motto: "We've gotta be brave, keep our tentpoles and keep it moving!") While the Broadway show featured 21 songs ‒ co-written by Nell Benjamin and Fey's husband, Jeff Richmond ‒ the film has just 13, two of which are new from Rapp, 23.

"I was so excited because I've never done anything like that before," says Rapp, who also played Regina on Broadway. "So much of my life these past six years has been surrounded by theater, but I've only written pop songs."

Last year, Rapp spoke out about her, at times, negative experience doing “Mean Girls” on Broadway and being body-shamed behind the scenes while she was also struggling with an eating disorder. Once she learned those same people would not be involved with the film version, it was “an immediate no-brainer” to sign on.

“It felt very much like a reclamation of that experience,” Rapp says. “This came at a really good time for me and my mental health.” Plus, “Tina has always been such a mom to me, and has always taken care of me and looked out for me.”

New 'Mean Girls' stars fill 'giant shoes' of original cast

The original film's cast has sweetly shown support for the new Plastics: Lohan posed with Rice on the red carpet at Monday's New York premiere, while McAdams told Entertainment Tonight that Rapp can't do "any wrong" as Regina.

"These guys absolutely filled these giant shoes that were given to them," Fey says. "I can't wait for people to see them in this movie."

As for the next stop on her own “Mean Girls” journey, the nine-time Emmy winner is currently updating the stage musical for a London production in June. With any luck, she'll still be putting "new twists" on this story when she's 80.

“I mean, God willing,” Fey says with a grin. “After London, maybe we’re good. But who knows? ‘Mean Girls on the Moon?’ ‘Mean Girls: Space,’ where it all takes place on a space station? Can we pitch that today?”

What day is it?Here's how fans made the October 3rd 'Mean Girls' Day happen.