Born in 1917, she is Grandpa's fraternal twin sister. Mitzi's older than Phil by 6 minutes. Their grandfather died in 1921. Phil and Mitzi stopped talking to each other when their pet dog Pooter died after being hit by a milk truck in 1927. However, Phil and she eventually reunite and Arnold puts a wonderful photo album of all three of them together.
Mitzi's only appearance was in the episode "Grandpa's Sister."
On August 20th 2012, Mitzi's voice actress Phyllis Diller passed away after a string of health problems.
- 76a. "Grandpa's Sister"