Did Darth Vader know that this character was his daughter from the start?
When Darth Vader and Princess Leia meet on board the Tantive IV in Star Wars Episode IV: A New Hope for the first time, does Darth Vader know she's his daughter?
@Chad: That's a very good point. I think it's settled then that Darth Vader didn't know Leia even existed prior to ROTJ, but Yoda's quote "No. There is another" has always confused me. Either in ESB it was already known that Leia would be revealed as Luke's sister, or they're talking about someone else. I find the prior to be more believable.
Two things to note, which don't justify another answer. i: In EP IV he doesn't think the children survived, he assumes that he Killed both his wife and children (child even don't know if he realized there were two) ii: They are not Vaders children they are Anikins they are part of who he was not what he has become the fact they exist may start his turning against the emperor.
At that point he doesn't even know Luke is his son and that's what starts his interest in finding "Young Skywalker."
He shows his surprise at learning that Luke has a sister in Return of the Jedi when he says he sees Luke's feelings are strong for his friends – then adds, in surprise, "Sister."
Wookieepedia states (when describing the duel between Luke and Vader on the new Death Star):
Vader, who had been probing Luke's thoughts, discovered that besides Luke he also had a daughter: Leia Organa
However, no attribution for this assertion is given in the article.
You bring up a good point: at the point when Vader says "Young Skywalker" wouldn't he have a pretty good idea Luke was his son? Same last name; age matches pretty well; powers are suspiciously Jedi ish. Or is Vader's mind so addled by the dark side he can't suss out familial relationships?
@zipquincy He dosn't make the connection, or at least pretends not to, until the emperor talks to him about it in EP V,