"Fifth Marx brother" appears with Donna
Margaret Dumont (October 20, 1882 – March 6, 1965).
Margaret Dumont was an American stage and film actress. She is best remembered as the comic foil to the Marx Brothers in seven of their films. Groucho Marx called her "practically the fifth Marx brother".
Margaret guest-starred on The Donna Reed Show in “Miss Lovelace Comes To Tea” (Season 1, Episode 34).