David Letterman chats with Cher on 'The Late Show with David Letterman' Tuesday Sept. 24, 2013.
FILE - This Feb. 6, 2013 file photo shows actress Lindsay Lohan attending amfAR's New York gala at Cipriani Wall Street in New York. Lohan will be a guest on "Late Show with David Letterman" next week. CBS says she will pay Dave a visit on the April 9 telecast. It will be her first "Late Show" appearance in six years. Lohan is promoting her guest appearance on the FX sitcom "Anger Management," which will air two days later. On that episode, she will be playing herself but as a therapy patient of series star Charlie Sheen. (Photo by Evan Agostini/Invision/AP, file)
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David Letterman sits at his desk on "Late Night with David Letterman" in 1986. .
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David Letterman and Oprah Winfrey
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Snoop Lion leaves "The Late Show with David Letterman" at Ed Sullivan Theater on April 25, 2013 in New York City.
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Late-night talk-show host David Letterman
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Comedians David Letterman and Jay Leno
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TV's David Letterman
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Sen. John McCain talks with host David Letterman.
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Britain's Prime Minister David Cameron talks with the CBS Late Show host David Letterman during the September 26, 2012 taping in New York in this September 26, 2012 handout photo.
Comedian Sarah Silverman leaves a taping of the "Late Show With David Letterman" on Monday Oct. 13, 2008, in New York
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Paul Reubens in front of CBS studios after a taping of The Late Show with David Letterman
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Robert (Joe) Halderman, left, at his arraignment for an alleged blackmail plot against late-night host David Letterman in New York on Oct. 2, 2009
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In this photo released by CBS, Sen. John McCain speaks to the audience while talking with CBS Late Show host David Letterman on Dec. 11.
The Edge, Larry Mullen Jr., Bono and Adam Clayton of U2 perform their first of five consecutive nights on 'Late Show with David Letterman' at the Ed Sullivan Theater on March 2, 2009 in New York City.