Inside David Letterman’s Retirement Announcement Show: ‘It’s a Madhouse’

News of Late Show host David Letterman's retirement was met with mixed emotions at the Ed Sullivan Theater in New York City on Thursday.

"People seem to have a mix of excitement to be here but are also really sad because of the announcement. One page told me: 'But he's 67, he's been doing this for a long time,' " an attendee tells The Hollywood Reporter of the mood inside the building. (Letterman turns 67 on April 12.)

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Meanwhile, news crews descended outside the theater almost immediately after news broke of Letterman's impending Late Show departure in 2015. "It's a madhouse like never before -- tons of news vans are outside. [Guest] Johnny Depp was signing autographs for a massive crowd, bigger than usual," the same audience member recalls of the mayhem outside.

Letterman opened Thursday's show by announcing that after more than two decades as host of the Late Show, he would be leaving at the end of his contract -- receiving a standing ovation. Word first broke when REM's Mike Mills, a guest on Thursday's show, announced the news on Twitter.

Letterman continued to make jokes about his retirement from the Late Show in his second taping. (Late Show tapes two shows on Thursdays.) That episode, which features Billy Crystal, Tony Hale and musical guest Liv Warfield, will air Friday.

"A year from now, I'll be on a beach with a metal detector," Letterman joked. Continued references to his end date, which has yet to be set, ensued: "This weekend, my son is taking me to see senior centers," "My retirement will not become official until [Survivor host] Jeff Probst blows out my torch" and "It's been tough doing this show since Regis [Philbin] passed away."

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Meanwhile, Crystal noted that 2014 was off to a bittersweet start: "With you retiring and Derek Jeter retiring, this is a really sad year."

And when Crystal asked Letterman about what Letterman's departure meant for his longtime bandleader Paul Shaffer, Letterman had a relatively bright outlook: "Oh, he'll be alright."

Letterman has been the first and only host of Late Show since it began on CBS in 1993, filming more than 4,000 episodes and conducting thousands of interviews.

“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,’” Letterman told his studio audience during Thursday's Late Show taping.

He added: "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.”

Letterman's departure announcement comes after he surpassed Johnny Carson as the longest-running host in late-night TV history, including his stint on NBC's Late Night.

Philiana Ng