During the special, plenty of the show's beloved supporting stars pop in to say hi, whether it's in person, like Tom Selleck, who played Monica's boyfriend, Richard, and Maggie Wheeler, who played Chandler's on-again off-again girlfriend, Janice, or via video chat, like Reese Witherspoon, who played Rachel's sister, Jill, and James Michael Tyler, who played bitter barista Gunther.
But the two-hour event is also a tribute to the show's millions of fans, all around the world. A segment featuring Pakistani activist Malala Yousafzai and mega-famous K-pop group BTS highlights Friends fans from different countries, who have embraced the show as a way to learn English, find new pals or just enjoy a few hours of entertainment.
And of course, Friends has plenty of celebrity fans, too, some of whom get to share their thanks with the cast and creators in special segments throughout the reunion.
Here's a look at the fun stars and famous faces who popped up to celebrate one of the greatest sitcoms of all time in Friends: The Reunion:
The massively popular K-pop boy band declare, "We love Friends!" in the international segment of the special, with RM opening up about why the show means so much to him.
"My mom bought me DVDs of the whole series when I was in elementary school," he shares. "Friends really had a big hand in teaching me English, and the show really taught me things about life and true friendship."
Cindy Crawford, Cara Delevingne and Justin Bieber
Corden surprises the cast with a "Friends reunion fashion show," which includes several A-list stars modeling some of the show's most memorable looks.
...Justin Bieber appears as Ross' infamous hybrid Halloween costume, "Spud-nik..."
...and Cara Delevingne pulls double duty, first modeling Rachel's Pepto-abysmal bridesmaid's dress, and then returning as the Holiday Armadillo!
"I'd have to say, I'm most like Monica, because I'm a clean freak," the soccer star declares, as he opens up about one of his favorite Friends memories, the iconic season 2 bottle episode, "The One Where No One's Ready."
"I travel a lot. I'm always in hotels, I've always got downtime," Beckham shares. "When I'm missing the kids, when I'm missing the family, I put on Friends... It's one of those episodes that when I'm away and when I'm feeling a little bit low, I just put it on, and it makes me smile to almost the point of crying."
"I can't quite be specific about which one, but I know I'm part of the Geller family," the Game of Thronesstar admits. "I'm incredibly anal, I'm neurotic as hell, and I wear overly tight trousers."
Jon Snow may no nothing, but Harington is crystal clear about why he loves the show so much.
"One of the reasons that Friends is so funny is the fact that these six actors are masters of physical comedy," he explains, calling out the oft-quoted "Pivot!" scene from the season 5 episode, "The One With the Cop."
"The thing about that scene is, it's so simple," he continues. "If you were to see it on the page, initially, it's three actors carrying a couch up a stairwell. There's maybe a page of dialogue, and nothing really in that dialogue suggests anything massively comic. But what they do in that time, in carrying that couch up those stairs, is one of the funniest things I've seen on TV."