Linda Duncan is the paternal grandmother of PJ, Teddy, Gabe, Charlie, and Toby. She is the mother of Bob, and the ex-wife of Frank. She made her first real appearance in Welcome Home and a gag appearance in Dress Mess. She is portrayed by Shirley Jones.
- She lives in Phoenix, Arizona.
- Her real name is Linda, rather than Gladys as said in Dress Mess, because in Welcome Home, she makes her first real appearance and is referred to as Linda.
- She and Frank Duncan are split up prior to It's a Charlie Duncan Thanksgiving
- It is possible that Linda's last name is not Duncan as she divorced her husband, Frank Duncan, and may have changed back to her maiden name which is currently unknown.
- She has a bit of a habit with using the words "what not" way too much to the annoyance of her daughter-in-law Amy.
- Oddly in A Duncan Christmas, she has gray hair when in Welcome Home she has blonde hair. The blond hair was possibly a wig.
- Her and Amy hate each other, but in A Duncan Christmas, they sing Deck the Halls with each other.
- She may still be alive by 2023 to see her great-grandson Gabe Jr., as Charlie is still trying to get Toby to move in with their grandma. However Charlie could have been referring to her maternal grandmother.
- In Dress Mess, in the ending credits, Linda was portrayed by Eric Allan Kramer, but was named Gladys, and was meant to look exactly like Bob. She asked the Doctor what gender her new grandchild will be. She looks like Bob but has grey hair, wears pink and carries a handbag with glasses. The doctor assumed she was Bob in disguise but then Bob came out with Gladys. These ending credits where just a joke and were not meant to be true.