Vader:
"Obiwan never told you what happened to your father?"
Luke:
"He told me enough! He told me you killed him!"
Vader:
"No! I am your father!"
(play John Williams score here)
Luke:
"no,NO!! that's not true!! thats impossible!!"
Vader:
"search your feelings you know it to be true!"
Luke:
"NO!! NO!!!!!!"
one of the great all time movie plot twists