As I mentioned, Chad Mitchell left the group himself, in 1964. He was replaced by John Denver, and the group became known as the just Mitchell Trio. In the late 1960s, the other two core members -- Mike Kobluk and Joe Frazier -- departed the group, as well, over a period of a few years and also left the music industry. While they were in turn replaced, Denver eventually left too for his highly-successful solo career. And the Mitchell Trio at this point had three totally different members than they started out with.
Then two decades after leaving the group to try for his own solo career, which was only moderately successful, Chad Mitchell reunited with Kobiuk and Frazier for the TV special, which is the subject of this video. They're terrific together, in great voice, even after all that distance of time, but what's especially fun is that that's not the only reunion in this reunion video -- because Chad Mitchell's replacement John Denver joins them, as well.
Mitchell gives a very affectionate introduction and then graciously walks off to let the second incarnation of the trio perform together as they all those years earlier. I have to believe that he eventually returned and that all four members of the "trio" sang together at some point in the show, but this is all I've been able to track down. Still, it's a treat to see.