10 Movie Endings Actors Didn't Know Were Going To Happen
5. "I Am Your Father" - The Empire Strikes Back
David Prowse physically portrayed Darth Vader in the original Star Wars trilogy, while the voice was of course dubbed during post by James Earl Jones.
And in the case of The Empire Strikes Back, George Lucas went to great pains to conceal the climactic revelation during Vader and Luke's (Mark Hamill) battle on Bespin - that Vader was Luke's father - enough that only himself, Mark Hamill, and director Irvin Kershner actually knew about it.
The shooting script for Empire instead had Vader tell Luke that Obi-Wan (Alec Guinness) killed his father, ensuring that David Prowse certainly had no idea he was actually taking part in what would become one of the most iconic plot twists in cinema history. The real line was then dubbed in by Jones.
Though it's been suggested that Prowse spoiled the Vader parentage twist to the press two years before Empire's release, in recent years this has been dismissed as Prowse making an off-the-cuff joke that coincidentally happened to be true, given that Lucas kept the twist so secret during shooting.