During production, great secrecy surrounded the fact that Darth Vader was Luke's father. Like the rest of the crew, Prowse—who spoke all of Vader's lines during filming—was given a false page that contained dialogue with the revelatory line being, "No. Obi-Wan killed your father." Hamill was informed just moments before cameras rolled on his close-up by director Irvin Kershner, and was told that he would be one of only three people to know the twist (the other two being Kershner and Lucas); therefore, if the news were to leak, they would know the source was Hamill. Hamill did not tell anyone, including his wife; according to Hamill, Ford did not learn the truth until he watched the film.