Moore died on Wednesday in Greenwich, Connecticut, of cardiopulmonary arrest after contracting pneumonia, the actress' rep confirmed to ET. She was 80.
White and Moore starred together on The Mary Tyler Moore Show in the 1970s, and Moore spent her last television appearance guest-starring on White's TV Land Sitcom, Hot in Cleveland.
"It's wonderful, but it makes me sad too. It makes me feel, well, why don't I have this in my current life?" Moore told ET of the reunion, which also featured Valerie Harper, Cloris Leachman, and Georgia Engel, at a press conference for the special episode.
"Where are all these friends, buddies, and co-workers, and people who loved each other? Why can't they be around?" she continued. "Or maybe they can."