This is from Barry Manilow’s third TV special (circa 1979). Their reaction at the end looks like even they were surprised how well the duet turned out.
Whenever I hear Barry Manilow, I cannot help but think of the Goldie Hawn and Chevy Chase film Foul Play (which is one of my favorite late 70’s comedies).
Here is a track from the very rare 1980 vinyl only release of “Cylon Love Songs”. This album is very difficult to locate nowadays. So it is a real shame this has not been released on CD or as a digital download.