The 54-year-old former first lady stopped by The Tonight Showon Tuesday, where she and the 44-year-old late-night host surprised some fans at 30 Rockefeller Plaza in New York City.
"We're about to surprise some people. They're going on a tour of 30 Rock -- they think they're going on a tour of 30 Rock -- and they're going to stop on the wrong floor. This floor," Fallon explained. "And that's where we step in."
The duo began their hilarious surprise by sitting in chairs and reading each other's books -- Fallon's Everything Is Mama and Obama's Becoming. When the elevator stopped, the pair dropped their books, eliciting excited cheers from the lucky riders before the door quickly closed.
The stunt continued with a magic trick where Fallon dropped a sheet to reveal Obama, a sing-along of "Jingle Bells" and Fallon opening a huge box to reveal Obama inside. One of the biggest gasps from a group came when Fallon tried to step on an elevator only to step off, causing Obama to come forward and question why he wasn't getting on.
Fallon and Obama's bit came to an end in spectacular fashion when the the elevator opened to find Obama casually jumping rope with a little help from the late-night host. The pair tried to top that by doing the sprinkler dance, but were sorely disappointed when the doors opened to reveal an empty elevator.
Obama was on the show to promote her book Becoming. The former first lady admitted that she left out plenty of good stories from the memoir, largely to speed up husband Barack Obama's reading time.
"I could've done a whole book on just the White House years, because there's so much stuff that happened, just unpacking all of that... The book would be 800 pages, and then it would take Barack, like, 800 days to read it," she quipped.
During the interview, Fallon held up a photo of the Obamas waving as they departed Washington, D.C., after Donald Trump's inauguration.
"Bye, Felicia," Obama joked of her thoughts in the photo, before revealing how her daughters -- Sasha, 17, and Malia, 20 -- reacted to leaving the White House.
"A lot was going on that day. That was a day," Obama said. "And right before that, my daughter's friends decided they needed a sleepover for the last day. I was like, 'Are you guys kidding me? We're leaving! You've got to take all your stuff, pick it up. The blankets, the bears.' They're all crying and I was like, 'Get out! We've got to go.'"
Watch the video below to see what happened during Obama's last Fallon appearance: