The Cheerful Charlies
Very proper head butler Charles Carson (Jim Carter) is briefly blackmailed by his old song 'n' dance partner, Charles Grigg (Nicky Henson). He hands Lord Grantham a poster from 1897 with the name of this, their old act, headlining on it. Lord Grantham sends Grigg packing. Carson is mortified, but keeps his job and his secret past is kept secret.
For fun, other names on the poster are: Bros. Ellis, Danny Sold, Miss Ada A, Albert C., Mr. Simpson, Tall Daisy, Florie Flower, Claudet Emerson, Terrible Tilly, and Small George. With the variety act nature of a show like that, no telling who sings and who has some other act.