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Before she died she was very sick.
It is unknown how long Rosemary and Gary Chalmers were married, or long ago she died, but they were evidently deeply in love as he remembers her with great fondness. When the Theodore Roosevelt study group was on an overnight trip in Springfield Forest, Chalmers told Bart that mornings were when he missed her the most.
Chalmers has two framed photos of himself and Rosemary together on display in his house. One of the photos shows the two of them at the beach.