I assume you are talking about the episode where Homer is constantly shrieking because a repressed memory revealed by a hypnotist? Homer finds the corpse of Smithers Sr. who died preventing nuclear accident but Burns tells Smithers Jr. otherwise.
Smithers: I'm glad to know he died a hero, instead of...that other way.
Burns: I told Smithers his father was killed by a tribe of savage women. I hope it didn't affect you in any way.
Smithers: We'll never know.