On Thursday, April 3, David Letterman announced his retirement after 33 years as a late night host. The news garnered loving respect for his more than three decades in the industry, as well as some speculation as to who might take his place. With their latest couch gag, "The Simpsons" continued that deliberation (and also managed to send up a touching tribute in the process). Just to be clear, this is (as Mashable noted), the longest-running scripted show honoring the longest-running late-night talk show host. Check out the clip above.