In 1938, Duncan appeared on the London stage at the Theatre Royal, Drury Lane in C.B.Cochran's musical production The Sun Never Sets.

The cast included fellow American Adelaide Hall, Leslie Banks, Edna Best and Stewart Granger.

After the London run closed, Duncan and Adelaide Hall from the original cast toured Britain with the production.

[1] While teaching at Howard, he continued touring as a soloist with pianists William Duncan Allen and George Malloy.

[8] In 1954, Duncan was the first to record "Unchained Melody", a popular song with music by Alex North and lyrics by Hy Zaret.

The recording was made for the soundtrack of the obscure prison film Unchained, in which Duncan also played a minor character.

Among his notable pupils was operatic bass Philip Booth who was a mainstay at the Metropolitan Opera for two decades.

[11] He died of a heart ailment at his home in Washington, D.C., February 28, 1998, survived by his wife, Gladys Jackson Duncan, and adopted son, Charles, a successful attorney.