David Letterman

David Letterman is seen during a taping of the "Late Show with David Letterman" on Wednesday, April 2, 2014, in New York.

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Late-night TV's longest-running host is announcing his riding off into the sunset. David Letterman announced his retirement as the host of CBS' "Late Show" during this afternoon's taping of tonight's broadcast. He will remain host until 2015, when the two-year contract he inked in 2013 expires. 

The news was first broken via a tweet from Mike Mills, bassist of R.E.M. through their breakup in 2011. Mills was on hand as the night's musical guest, performing with singer-songwriter Joseph Arthur.

When Letterman broke the news, he mentioned calling CBS president/CEO Leslie Moonves earlier today to thank him for his support. While he assured he'll be staying with the program into 2015, he was unsure of his particular end date. After delivering the news, Letterman received a well-deserved standing ovation from the studio audience.

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Letterman's exit will provide yet another jolt to the late night talk show landscape, which underwent a massive transformation earlier this year with Jimmy Fallon replacing long-time leader Jay Leno as the host of The Tonight Show. Seth Meyers took over for Fallon on "Late Night" in late February, exiting from his role with NBC's "Saturday Night Live."

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Letterman has been with CBS' "Late Show" for the past 21 years. His retirement was confirmed via the following official statement from his representative:

David Letterman, during a taping of tonight’s Late Show, said that he informed Leslie Moonves, President and CEO of CBS Corporation, that he will step down as the host of the show in 2015, which is when his current contract expires.

“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,’” said Letterman.

“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,” he added, to a standing ovation from the audience in the Ed Sullivan Theater.