Let's Sing Out, October 1966. Gilbert & Sullivan's "Prithee, Pretty Maiden" written for the Opera, Patience. Host, Oscar Brand, duets with Joan Anderson (Joni Mitchell).
It's just exhibit z-452 of how good Gilbert & Sullivan were. They wrote a pastiche of an English folksong, the likes of which were passed down to the American folkies, so it fits extremely well in that genre.