The 22-year-old actress was just 10 years old when she starred opposite LeBlanc in 2004.
Dakota Fanning may be a movie star now, but in 2004, she was just a guest actor on Friends!
Twelve years later, the 22-year-old actress has nothing but fond memories of her experience on the hit sitcom, gushing all about it on Thursday's Live! with Kelly.
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"Matt LeBlanc was here, and you worked with him," Ripa asked Fanning during her interview.
"I did, yeah. I was on the last season of Friends for an episode, and all my scenes were with Matt," the American Pastoral star answered. "I think I was nine or 10, something like that."
"Did you see him backstage?" Ripa inquired, setting up for the surprise reunion.
"I didn't, but I would love to. I remember meeting him…" Fanning said, before spotting LeBlanc emerging from backstage.
"Long time, no see! You're so big. You were like this when I saw you last!" LeBlanc adorably yelled while greeting his former co-star. "Congrats on everything. So nice to see you!"
"I was so starstruck meeting everyone in the cast," Fanning explained. "I still remember it, and I remember talking to Matt in the breakfast area on the stage, like, on a rehearsal day. And he was asking me something -- I don't remember what you were asking -- but I was not answering, or saying like, not the right response. And I remember my mom was standing next to me, and I looked up at her, and she was like, 'What has happened to you? Like, what is wrong?'"
See the rest of their sweet reunion in the video below:
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The former co-stars also posed together for a photo to commemorate the occasion.
Fanning isn't the only Friends co-star LeBlanc has reunited with lately. ET caught up with the actor in August, where he dished all about filming his new show, Man With a Plan, just steps away from Matthew Perry's The Odd Couple on the CBS Radford lot in Studio City, California.
"That's great to see him there and it's funny to see him on a lot and not run lines with him," he shared. "It's just strange for me."
"It's like, 'What scene are you -- why are you out here? Oh no, no, no, you're on a different show now!' That was 20 years ago, nevermind!" he added.
WATCH: Emilia Clarke Adorably Fangirls Over Matt LeBlanc, Asks Him to Say 'How You Doin'?'
See more in the video below.