Jennifer Garner is letting fans in on some behind-the-scenes details from the set of one of her most classic roles.

During a recent Q&A session with theSkimm, the actress revealed why one scene almost made her 13 Going On 30 costar, Mark Ruffalo, quit.

“We started to learn the dance,” she said, recalling the big sequence in the movie where a bunch of party-goers perform Michael Jackson’s ”Thriller” choreography. “Our first rehearsal, I think it was like Mark, Judy [Greer], and me, and Judy and I were both dancers growing up and poor Mark didn’t know that and he came in and hated the rehearsal process so much, he almost dropped out of the movie.”

Obviously, Mark didn’t end up quitting, going on to nail the final dance that made its way into the film. Plus, it turned out to be a cult-classic film that fans still reminisce about all the time.

Of course, we’re not the only ones who can’t get enough 13 Going On 30--the cast of the movie loves it, too, and make regular callbacks to the 2004 film.

At the top of the year, Garner shared a photo of herself alongside her on-screen frenemy, who is actually one of her best friends in real life.

“Always the smartest. Always the funniest. Always the biggest @dodgers fan in the room,” she wrote in the Instagram caption. “I love @missjudygreer. #TeamJG. p.s. Hey, JG — remember how I said I wasn’t going to post you? 😬 Sorry, but you’re cute.”

Even more recently, Jennifer reunited with Mark Ruffalo in Canada on the set of The Adam Project, a film both actors star in alongside Ryan Reynolds and Zoe Saldana.

Once they began filming in February, the pair commemorated the occasion with a selfie, which the actor captioned, “Reconnecting with an old pal. Anyone know where we can get Razzles in Canada?”

Jennifer shared the same snapshot and wrote, “Wishing dust worked! And I got a perfect day with my old pal.”