The team of Dean Martin and Jerry Lewis split up in 1956, playing their last engagement together on July 25 of that year, ten years to the day after their first booking as a duo. Over the years, they received many offers to appear again together — if only for one performance — but the offers were never accepted. Many would tell you that the next time the world saw them on the same stage was September 5, 1976 when Dean made a surprise appearance on that year's annual Jerry-hosted telethon to combat Muscular Dystrophy.
I linked to a pretty good video of that reunion in this message and then we had a more detailed discussion of the moment in this message.
Ah, but was that really the first time the two had appeared together since the split? No, there were a couple of other encounters, one reportedly on an Eddie Fisher Show in 1958. The word was that Eddie and guest Jerry were screwing around and then Dean and Bing Crosby did a brief walk-on. The stories of this alleged moment made it sound like it wasn't planned; like Dean just happened to be in the studio while Eddie and Jerry were doing a live show and Dino decided to poke his head in for a sec.
I never saw this video and the people I heard about it from had never seen it, either. Some of us kinda doubted its existence but it has now turned up and you can watch a not-great clip of it below. A couple of points: The clip is twelve minutes long and not very funny except for the few seconds when Dean pops in, about six minutes into it. There's time code on the video and Dean enters at 03:24:53:05 but if you're going to watch just for that moment, start watching a minute or so earlier so you get the context.
Secondly, it's obviously a planned bit which Jerry was expecting. I think the closest thing to a real surprise was that it looks like Dean was supposed to enter earlier so Eddie and Jerry had to ad-lib and stall until he could actually make his entrance. Bing Crosby, who then might well have been the biggest star of the four, goes mostly unnoticed. Thanks to Dan O'Shannon for alerting me to this…