David Letterman called rival host Jay Leno the "most insecure person I have ever known," during an interview with Oprah Winfrey for "Oprah's Next Chapter."

The "Late Show" host told Oprah his rivalry with Tonight Show host Jay Leno did not start when Dave was passed over for Johnny Carson's old seat, contrary to what has been said of the late-night wars of the past.

"We were always friends before all of this happened," Letterman told Oprah in the interview. "He has a way ... he's an unusual fellow. I've never met anyone quite like Jay. And I will say, and I'm happy to say, that I think he is the funniest guy I've ever known. Just flat out, if you go to see him do his nightclub act, just the funniest, the smartest, a wonderful observationist and very appealing as a comic."

"The fact that he is also maybe the most insecure person I have ever known ... I could never reconcile that," Letterman added in the preview released today.

Letterman and Leno have been rivals for many years. They reportedly met in 1975 and worked together for a few years. Initially they admired each other, Letterman was impressed with how comfortable Leno controlled the stage and Leno thought Letterman possessed the most original material on the comedy scene, according to the book "I'm Dying Up Here" by William Knoedelseder, an account of the 1970's stand-up comedy scene.

However in 1992 Leno became the host of "The Tonight Show," Letterman's dream job, according to reports and they never spoke again.

Over the years, Letterman and Leno mock each other in their late night shows increasing ratings between the shows and leading some people to chose sides in the TV ratings battle.

According to ContactMusic.com, nearly 10 years ago in 2003, Leno said he "owed" his career to Letterman.

"I owe my career to Dave. It has been 11 years and everybody's rich, everybody's successful. Come on."

Leno reportedly tried to reach out to his rival and make peace but Letterman never replied.

Leno told GQ Magazine in 2009 that he wrote a letter to Letterman to solve their issues but the "Late Night" host did not reply.

Letterman's interview with Oprah airs on January 6.

Letterman on Leno: "He Is The Funniest Guy I've Ever Known" — First Look

Despite what's been said about the late-night wars of the past, talk show host David Letterman tells Oprah his rivalry with Tonight Show host Jay Leno did not start when Dave was passed over for Johnny Carson's old seat. Watch as he reflects on his old friend and reveals why Jay is the funniest guy he's ever known.

Watch Oprah's interview with David Letterman on Sunday, January 6, at 9/8c.