Let’s talk about “13 Going on 30”—aka one of the most classic rom coms to ever come out of 2004. Jennifer Garner is absolutely brilliant as the 13-year-old girl named Jenna stuck inside a 30-year-old’s body.

One day Jenna’s an early teen, getting teased at her own party by a bunch of popular girls who she so badly wishes to be friends with. She locks herself in a closet after a terribly embarrassing moment with a boy, wishing to just be 30 already so she could be passed her frustrating high school days.

What Jenna doesn’t realize is that her wish was about to actually be granted, thanks to her best friend Matt gifting her wishing dust for her birthday—the dust that fell over her as she was wishing so badly to be older. Poof: She wakes up in her unrecognizable New York City apartment ready to go to work as a magazine editor—her dream since she was 13!

As a 30-year-old, Jenna realizes that she isn’t friends with Matt anymore, so she goes on a mission to find him. When she does, he tells her that she had ditched him years ago to be friends with those popular girls she wanted to be close with.

Matt is played by actor Mark Ruffalo, who does a phenomenal job taking on the role of the 30-year-old himself who’s contacted by his long-lost best friend. In fact, one classic scene in the film is when Jenna invites Matt to a work party, which he attends only to be suckered into dancing to Michael Jackson’s “Thriller”—a song and dance that was popular when Jenna and Matt were 13 (so naturally it’s fresh inside Jenna’s head).

In the movie, the two wind up saving the party’s ho-hum vibe by breaking out on to the dance floor to dance to the song. In the movie, Matt is hesitant to join in at first—and apparently, so was Mark in real life!

During a recent interview for theSkimm, Jennifer revealed that Mark nearly quit the movie after the first dance rehearsal for the iconic dance sequence!

“Our first rehearsal, I think it was Mark and Judy [Greer] and me, and Judy and I were both dancers growing up and poor Mark didn’t know that,” Jennifer said. “And he came in and he hated the rehearsal process so much he almost dropped out.”

When People posted about what Jennifer said on their Instagram, Mark weighed in for a bit more context.

“It didn’t help that it took me 3 hours to learn what Jen mastered in about 20 minutes!” he wrote. “Matty had to be dragged out on that dance floor as well, poor guy. But all this time later he is grateful he did!”

So are we—we can’t imagine the movie without Ruffalo!

Want to reminisce about the dance he almost backed out of? Check out that classic dance from the movie below!

Are you a 13 Going on 30 fan? Who do you think would’ve played Matt if Mark had quit the film?