Conan O’Brien says he owes a lot to David Letterman. On Wednesdays’ episode of TBS’ Conan, O’Brien recalled the pressure he was under when he took over NBC’s Late Night from Letterman in 1993. Conan was worried his show was going to be canceled but four months in, Letterman called up and said he would like to be a guest on O’Brien’s show. “It was like the Beatles asking Maury Povich if they could stop by and sing a few tunes. At the time, I was convinced it was a prank —- it couldn’t be real. But, on February 28, 1994, David Letterman walked onto my set and blew the doors off the place. It’s easily one of the happiest nights of my professional life,” O’Brien said. Letterman ends his 33-year run on late night TV Wednesday on CBS. O’Brien said he will alert viewers to switch the channel to CBS the moment Letterman’s Late Show begins.