David Letterman announced his impending retirement during a taping of tonight's "Late Show," saying he'll bow out of the CBS talk show in 2015. (The news was broken on Twitter by, of all people, R.E.M. bassist Mike Mills, who was at the taping.)

During the taping, he said the following:

“The man who owns this network, Leslie Moonves, he and I have had a relationship for years and years and years, and we have had this conversation in the past, and we agreed that we would work together on this circumstance and the timing of this circumstance.  And I phoned him just before the program, and I said ‘Leslie, it’s been great, you’ve been great, and the network has been great, but I’m retiring.'

“I just want to reiterate my thanks for the support from the network, all of the people who have worked here, all of the people in the theater, all the people on the staff, everybody at home, thank you very much.  What this means now, is that Paul and I can be married.

“We don’t have the timetable for this precisely down – I think it will be at least a year or so, but sometime in the not too distant future, 2015 for the love of God, in fact, Paul and I will be wrapping things up.”

UPDATE: Moonves' own statement: 

 “When Dave decided on a one-year extension for his most recent contract, we knew this day was getting closer, but that doesn’t make the moment any less poignant for us. For 21 years, David Letterman has graced our Network’s air in late night with wit, gravitas and brilliance unique in the history of our medium. During that time, Dave has given television audiences thousands of hours of comedic entertainment, the sharpest interviews in late night, and brilliant moments of candor and perspective around national events. He’s also managed to keep many celebrities, politicians and executives on their toes – including me. There is only one David Letterman. His greatness will always be remembered here, and he will certainly sit among the pantheon of this business. On a personal note, it’s been a privilege to get to know Dave and to enjoy a terrific relationship. It’s going to be tough to say goodbye. Fortunately, we won’t have to do that for another year or so. Until then, we look forward to celebrating Dave’s remarkable show and incredible talents.”

Letterman would be stepping down 22 years after his "Late Show" premiere, and 33 years after he became a TV fixture as host of NBC's "Late Night." He was a trailblazer at NBC, and the defining comic voice of a generation — most of the current crop of late-night hosts are far more influenced by Letterman's snark and/or avant-garde comic sensibility than they are by either Johnny Carson or Letterman's longtime-rival Jay Leno.

His nightly Top 10 list is one of the most oft-imitated comedy bits in TV history, and especially in his early NBC days, he was a mad comic scientist, throwing watermelons from the roof of 30 Rock, performing stunts in a velcro suit or encouraging the many deranged characters of frequent guest Chris Elliott. He left NBC in 1993 after Leno inherited the "Tonight Show" job Letterman thought was his birthright, and for a time his "Late Show" dominated Leno's "Tonight," before becoming a steady second in the ratings for most of the run. In the CBS years, Letterman steadied in some ways, and became crankier in others, but he has more than risen to the occasion when it's called for. His monologue in his first show back after 9/11 is a thing of naked emotional beauty, as he admitted, "If we are going to continue to do shows, I just need to hear myself talk for a couple of minutes." His return from open heart surgery the year before was similarly touching and honest in a way the sarcastic Dave of NBC would have been very reluctant to be.

In retiring next year, Letterman would in theory be outlasting Leno, though it is extremely possible that Jay will have landed another TV gig well before Dave steps away. And there's the question of his successor. Once upon a time, Jon Stewart (who works for corporate sibling Comedy Central) seemed like the heir apparent, but it's become clear at this point that the only talk show he's interested in is his current one. "Late Late Show" host Craig Ferguson reportedly has right of first refusal, but we'll see if he wants a job that would likely be much more rigidly formatted than the loose conversations he's allowed to have. CBS could in theory go after Leno, but I imagine they want someone younger who can do the job longer. Would Stephen Colbert be interested in a job where he could get to be himself rather than "Stephen Colbert" every night? Does Conan have an out in his TBS contract, and even if he does, would CBS consider him damaged goods at this point? Might this finally be time for the network late night ranks to welcome a woman for the first time in a few decades? (Tina Fey could do some very interesting things with the job, though she'd of course be competing with her pal Jimmy Fallon.)

What does everybody else think? Are you sad Dave is stepping down? Relieved because you feel his heart hasn't been in it for a while? Do you want to see Craigy Ferg get the promotion, or would you prefer that he keep doing what he does so well at 12:35? And if not him, whom would you like to see succeed Letterman? Is it time for Louis C.K. to succeed Letterman for real?

Here's the full video of Letterman's announcement:

Alan Sepinwall has been reviewing television since the mid-'90s, first for Tony Soprano's hometown paper, The Star-Ledger, and now for HitFix. His new book, "TV (The Book)" about the 100 greatest shows of all time, is available now. He can be reached at sepinwall@hitfix.com