One great addition to Lester Flatt and Earl Scruggs' Foggy Mountain Boys occurred in 1949, with the addition of a mandolin player and tenor singer named Curly Seckler. Seckler would remain with Flatt & Scruggs until 1962. During this time, they recorded well over 100 songs and many still consider the 1950's Flatt/Seckler duets to be some of the best bluegrass music performances ever.
Here is a video that I wanted to share, that which I do not own, that will give an idea.