Yes, it's true—Darth Vader was never meant to be Luke's father. This is confirmed by the fact that the ghost of Anakin Skywalker appears in early drafts of the movie's script.
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In another familial twist, early drafts indicate that Luke has a sister, but not Leia. While these allusions were removed from the final film, there is still some debate over whether Lucas intended Leia to be Luke's sister by the time he finished making The Empire Strikes Back.
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Although it went on to become one of the Star Wars series' most iconic lines, Han Solo's "I know" wasn't part of the script—it was improvised by actor Harrison Ford who was unsatisfied with the written line, which was a simple "I love you too."
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Although many claim that is was just a joke taken out of context, George Lucas famously called The Empire Strikes Back the "worst" Star Wars movie. Ouch—you hit us right in the fandom, buddy.
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