Chad: That's a very good point. I think it's resolved then the Darth Vader didn't recognize Leia also existed before ROTJ, but Yoda's quote "No. Over there is another" has constantly confused me. One of two people in ESB the was already known the Leia would be revealed as Luke's sister, or they're talking about someone else. I find the before be more believable.
No.At that point he doesn"t also know Luke is his son and also that"s what starts his attention in detect "Young Skywalker."
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He reflects his surprise at learning that Luke has a sister in Return that the Jedi when he states he look at Luke"s feel are solid for his girlfriend – climate adds, in surprise, "Sister."
Wookieepedia says (when describing the duel in between Luke and Vader top top the brand-new Death Star):
Vader, who had been research Luke"s thoughts, discovered that besides Luke he additionally had a daughter: Leia Organa
However, no attribution for this assertion is provided in the article.
To re-use part of mine answer to an unrelated question Why perform we listen Leia's Theme throughout Kenobi's death?:
At the time of working of "A brand-new Hope" (e.g. Before 1977) - it to be NOT well-known to anyone (including Lucas) that Luke and also Leia space family. Due to the fact that Luke was Anakin Skywalker"s son from the start of ANH, that method Leia wasn"t intended to be his daughter, till at least mid-work on episode V.
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To be much more specific, even an early Leigh Brackett"s 1978 draft of "The empire Strikes Back" didn"t have actually that relationship created yet - that was introduced later (source).
Another related evidence for Luke and also Leia not yet being associated was 1978 pre-ESB book that to be a sequel come "ANH" - Alan Dean Foster"s "Splinter that the Mind"s Eye". It creates the design template of romantic interest in between the two (presumably, in part, since Foster and Lucas didn"t recognize if ANH would certainly be a large hit and if Harrison Ford would be interested in the sequel need to the sequel be based on "Splinter")