FARGO, N.D. — The mother of Democratic U.S. Sen. Heidi Heitkamp of North Dakota has died.

Heitkamp's brother, Joel, a popular Fargo talk show host, tells The Associated Press that Doreen Heitkamp died Sunday after a long fight with Parkinson's disease. She was 88.

Heidi Heitkamp posted on her Facebook page that her mother died on what would have been her 66th wedding anniversary. Doreen's husband, Ray, died in 1982.

The senator wrote that her mother was the "rock of our family" who often said her greatest achievement was that her seven children are each other's best friends. Heidi Heitkamp is the middle child.

Funeral services are scheduled for Thursday in Mantador, North Dakota.