You have a big story. I do. Such mixed feelings about this. But it is huge and stunning indeed. It is already shaking up the late night TV landscape. David Letterman announcing he is retiring this... See More
You have a big story. I do. Such mixed feelings about this. But it is huge and stunning indeed. It is already shaking up the late night TV landscape. David Letterman announcing he is retiring this important and fans are shocked that the longest serving late night host is, in fact, calling it quits. ? it started out like the windup to a good joke. I said, when this show stops being fun, I will retire ten years later. Reporter: But then the punch line made it clear this was serious. I'm retiring. This is really -- Yeah. This is -- you actually did this? Yes, I did. Reporter: David Letterman announcing his plans to move on after 32 years of late night laughs. We don't have the timing of this precisely down. It will be I think at least a year or so but sometime in the not too distant future. Reporter: His impending departure marking the end of an era defined by his signature top ten list. And the number one fun fact about gardening. With enough care and effort, you can grow your own barackoli. Reporter: His guests ranging from wild animals. Smells Ike an Orange. Reporter: To world leaders and everything in between. ? Reporter: There were tender moments as well. Letterman, the first late night comic to return to the air after 9/11. We've lost 5,000 fellow new yorkers and you can feel it. Reporter: Even bouncing back after emergency quintuple bypass surgery in 2000. Wait till you hear what happened to me. Welcome to taco bell. What do you want. Reporter: Now after more than 4,000 shows his surprise announcement is shocking fans who love him including ABC's own late night comedian jimmy Kimmel who tweeted "David Letterman is the best there is and ever was." Everybody at home, thank you very much. Reporter: But in the midst of this bittersweet moment that signature Letterman humor still shines through. What this means now is that Paul and I can be married. Reporter: A laugh and a standing ovation as the question now becomes, who will replace him? All right now, I think everybody is just going to miss him so much and so much reaction on Twitter this morning to Letterman's retirement. Ellen DeGeneres said "David Letterman announcing he's retiring in 2015. It's been 31 incredible years. Television won't be the same without you, Dave." Lena Dunham tweeted "I love Letterman but am I really excited about what this could mean for the diversification of late night. Trying not to be a pessimist." Ricky Gervais "Cheers to Letterman. A kingmaker and probably the man most to blame for inflicting me on America. See you soon" finally, we love this one, Albert brooks "David Letterman announces that he will retire next year. CBS frantically knocking for someone named jimmy." George, Amy, Ryan. What do you think? Sad, right? I know. From some of the others, Jon Stewart. He influenced so many. Boy, that is going to be some fight to fill that seat. It is going to be interesting to watch over the next year.
This transcript has been automatically generated and may not be 100% accurate.