January 28, 2015 10:16 AM EST

David Letterman “can’t wait” for retirement, the Late Show host revealed during a Tuesday interview with Regis Philbin, but not out of exhaustion from 33 years on the job.

Really, he said, it’s the exhaustion of explaining what comes next.

The gap-toothed late night mainstay will host the Late Show for the last time on May 20, after which former Comedy Central funnyman Stephen Colbert will settle into the host’s chair.

Read more: James Poniewozik on David Letterman and late night’s ‘greatest run’


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