In the months leading up to David Letterman's last night as host of "The Late Show," rumors flew about the possibility of Letterman's former late-night rival Jay Leno making an appearance. Letterman's departure came and went without even a single mention of Leno. Now, Leno finally explained the reason why he did not appear on Letterman's final show.

The reason went back to the time when Leno was preparing for his final episode of "The Tonight Show."

I asked Dave to do a 10-second tape for us [when I left]," the former host told AdWeek. "Anything, just...'Leno who?' They said no, they didn't want to do it. Well, why am I going to run all the way to New York? I mean, quid pro quo. I just said, 'No, that's kind of silly.'"

The last time Leno appeared as a guest on Letterman's show was May 1992, two weeks before he started hosting "The Tonight Show," according to Mediaite. The last time the two ever appeared on the same screen together was in a 2010 Super Bowl ad along with Oprah Winfrey.

Letterman and Leno began a bitter rivalry in the early 1990's when Leno won the job of "The Tonight Show" host over Letterman, according to CNN. That led Letterman to take the job hosting "The Late Show" over at CBS, which aired at the exact same time as "The Tonight Show."

Leno ended his run as on "The Tonight Show" back in February 2014.