"Obiwan never told you what happened to your father?"
"He told me enough! He told me you killed him!"
"No Luke, I was his lover!"
"NO! NO!! that's not true!! That's impossible!!"
"Search your feelings; you know it to be true!"
"NO!! NO!!!!!!"
...
ROTJ:
....
"Why didn't you tell me? You told me Vader betrayed and murdered my father."
"Your father was seduced by the Dark Side. When that happened, the good man who was your father was destroyed. So what I told you was true, from a certain point of view."