This question already has an answer here:
I remember knowing back in the mid-80s that Luke's father and Obi-Wan Kenobi fought on a lava planet which resulted in Luke's father being hurt badly enough to need the head-to-toe black leather outfit with cape and flashing lights that we knew already as Darth Vader.
But at that time, where would I have learned this from? Was it mentioned in one of the novel adaptations of movies IV, V or VI? Or am I just psychic?
It's been bugging me for 30 years now wondering how I knew this happened.