[philwelch]

I believe the actual shooting script for ESB omitted Vader’s admission that he was Luke’s father; the replacement line was “No, Obi-Wan killed your father”. The actual line, “No, I am your father” was kept secret and only shared with the actors on set when they filmed that specific scene.

[philistine]

Not all the actors. David Prowse, who played Darth Vader had no idea. Only Hamill knew. There were only four people who knew at that point. Lucas, Kasdan, Hamill and Kerschner.