We wrote many, many versions of this scene. Here's one we didn't use in the actual story.
This is the last intermission strip before Episode VI, which begins with the next strip.
Darth Vader: Obi-Wan never told you what will happen to you.
Luke: He told me enough. He told me... Wait. What will happen?
Darth Vader: Uh huh.
Luke: Um. I'm going to kill you?
Luke: Even though you're... my father!
Darth Vader: Actually, Luke, I am my father.
Luke: No. No. That's... Wait, what?
Darth Vader: And your father. Who is you.
Luke: That's... implausible.
Darth Vader: In a few years you will discover the secret of Force Time Travel.
Darth Vader: This secret was not meant for mortal minds to behold. Driven mad, you will turn the Dark Side, sire yourself, and adopt Gothic body armour. Do you like it?
Darth Vader: Never mind, of course you will.
Luke: Well this is all a little out of left field.
Darth Vader: No no, it has been foreshadowed. In the tree on Dagobah, it was your head inside the helmet.
Luke: Also, why were you hitting yourself?