What's My Line? - Ford Frick; Linda Darnell; Garry Moore [panel] (Mar 25, 1956)

And so begins a new phase of WML, in which the 4th panel slot is now a permanently rotating one. The same happened with Dorothy's spot after her death in 1965.
MYSTERY GUEST: Ford Frick [MLB Commissioner]; Linda Darnell [film actress]

PANEL: Arlene Francis, Garry Moore, Dorothy Kilgallen, Bennett Cerf