A lot of folks loved the "surprise" ending to the last installment of Newhart, the sitcom Bob Newhart did after he did The Bob Newhart Show. Here's the last nine minutes of that historic episode of Newhart. Unfortunately, this clip does not end, as the original telecast of it did, with the theme music from The Bob Newhart Show.
And here's a brief interview with Bob explaining how they kept it a secret. There are those who dispute that the idea originated with Newhart's wife but I don't want to get into that.