After 31 years on the air, David Letterman will be signing off. As you may have seen, the Late Show host surprised audiences last night by announcing that his time on the air is coming to an end. In a surprisingly emotional segment—laced with Letterman’s signature deadpan quips—the 66-year-old TV legend told a story about fishing with his son, and the realization that the time to retire from TV for good has come. Though there’s no official date set for Letterman’s final show, his current contract with CBS ends in August of 2015. Let the search for Jimmy Fallon’s new rival begin …