Sandler serenades the "Tonight Show" host, before spilling on his days at "SNL."
In celebration of Jimmy's five years fronting the show, the fellow "Saturday Night Live" alum kicked off his appearance by performing a parody song he wrote in honor of Fallon, called "My Jimmy Fallontine."
"I've known you since you were a little boy," he said before taking the mic, "I wrote you a song to tell you how much in love with you I really am."
"My Jimmy Fallontine, sweet little Valentine, you make me laugh when you slow jam the news," he then sang. "I think it's pretty cool, you've had the same haircut since middle school and you imitate me with your zaba daba do."
Sandler then expressed some jealousy over one of Jimmy's best friends, Justin Timberlake, as he finished off the song. "When there's drug tests at NBC, you give Questlove a sample of your pee," he continued, "Be mine for goodness sake, break up with Timberlake. This Jimmy Valentine, Happy 5 Years on TV. 11:35 Eastern Standard Time, too late for me."
Watch the performance below:
Sitting down for his interview, Sandler then talked a bit about his friendship with the late Chris Farley, who he honors with another special song during his "100% Fresh" standup special on Netflix.
"I was all around the country and every night I sing the Farley song, everybody loves the guy," he explained. "I sing in the Chris Farley song, we used to share an office and I talk about how I walked in one time, he had a walkman on and ... and he turned around and he looked up at me and his eyes were filled with tears."
Why the waterworks? Farley was listening to KC and the Sunshine band, which reminded him of his father and made him emotional.
Sandler also recalled one particularly memorable moment with his friend while doing a "Pepper Boy" sketch on "SNL" back in the day, where the comedian vowed to make Adam break character. Hearing this story, it sounds like he succeeded.