Jimmy Kimmel and Jimmy Fallon swap late night talk shows for April Fools' Day joke

There may be two Jimmys on late night, but they're both in on the joke.

On Friday evening, Jimmy Kimmel and Jimmy Fallon took part in an April Fools' Day joke that saw the dueling late night hosts swapping places, appearing on each other's programs.

Fallon, who hosts NBC’s The Tonight Show, popped up on Kimmel's program, Jimmy Kimmel Live on ABC. As Fallon took Kimmel's stage in Los Angeles, the audience cheered profusely.

"Hi, I'm Jimmy," Fallon told the surprised crowd, laughing. "Please settle down, you're going to offend the other Jimmy. Happy April Fools' Day everybody. I switched places with Jimmy Kimmel. But as far as surprises you've seen on ABC this week, this was a distant second," he said, referring to Will Smith slapping Chris Rock at Sunday's Academy Awards ceremony, which also aired on ABC.

"It's really strange for me to be here. I feel like someone opened a late night multiverse. Well, I hope you're happy to see me. I'm happy to see you," Fallon continued.

Soon, the host shared that Kimmel was actually in New York on the set of the Tonight Show.

"I'm worried my dad's gonna call me tomorrow and be like, 'I'm watching The Tonight Show. You've never been funnier,'" Fallon joked.

Fallon continued, sharing that he and Kimmel "worked really hard to keep this a secret," before going split screen to share the screen with Kimmel.

"A big chunk of your audience almost left when I walked out," Kimmel joked from New York.

After a bit more banter, Fallon shared how much he likes Kimmel. "I love that guy," he shared. "He's a great guy."

However, he added that the two get mixed up frequently.

"We really do get mixed up all the time. Really. People come up to me , they'll talk to me for 10 minutes, and as they're leaving, they'll say 'I can't believe I met Jimmy Kimmel,'" said Fallon.

The pranks didn't stop there, however. Later on in the program, Fallon brought out Kimmel's long-standing fake nemesis, Matt Damon. But instead of actually bringing out Damon, he brought out singer Justin Timberlake dressed as Damon, sporting a Boston Red Sox jersey and hat, Dunkin' Donuts cup, and blond wig.

"What are some of your favorite Boston spots?" Fallon jokingly asked Timberlake.

"Take the T to Harvard," Timberlake said when a heavy Boston accent. "Dunkin'. Boston, uhhhh, park. Cheers. Sometimes you wanna go where everybody knows I'm Matt Damon."

Later, Timberlake attempted to list the Jason Bourne movies in character, unable to do so.

To close out the episode, Fallon encouraged Timberlake to spray paint Kimmel's desk.

"Jimmy would really want something more from Matt Damon," Fallon joked. "So I was just wondering, could you tag his desk?"

Timberlake went on to emblazon the wooden desk with "I love Matt Damon" written in pink, playing up the host's rivalry with the mega-star.