This is from the 1968 season of The Red Skelton Hour, season 17 episode 25.

The young singers begin to perform Paul Simon’s song “Feelin’ Groovy” and then are joined by that evening’s special musical guest.

This video is also available on YouTube, but it names the special guest in the title, and I think it’s more fun if the special guest makes a surprise entrance. See if you recognize him after all these years.