"This Guy's in Love With You" was a Herb Alpert single written by Burt Bacharach and Hal David. It had been written years before and forgotten, but offered to Herb Alpert by Bacharach because Herb was looking for dusty treasures exactly like this song. It went to #1 on the Hot 100 and stayed there for four weeks. It's truly a beautiful song, but now mostly forgotten.
Watch the video, introduced by the Carpenters here.