Watch Jimmy Fallon's tribute to David Letterman

"Tonight Show" host Jimmy Fallon.

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Jimmy Fallon took a break from his usual "Tonight Show" antics on Monday night to bid farewell to David Letterman, who is signing off from the "Late Show" on Wednesday night.

"I, like every kid who grew up watching him, will miss him," Fallon said during the heartfelt tribute. He also noted how his eighth-grade teacher predicted he would take over for Letterman one day. (Close, but not quite.)

The most emotional moment came when Fallon recalled Letterman's words during his first show after the 9/11 attacks.

"The city was in shock, and we're all looking for answers, and we wanted to see what Dave had to say and we looked at him to say something," he told his audience. "He said, 'There's only one requirement for any of us, and that's to be courageous, because courage, as you might know, defines all other human behavior.'"

"David Letterman is courageous," Fallon said. "Have a nice retirement, Dave!"

Watch his entire Letterman salute below: