A question that has intrigued me for ages and newer knew the right answer. Vader in 'A New Hope' didn't had an idea that Luke is his son (or Leia is his daughter). Yet in the 'The Empire Strikes Back' both him and Palpatine know that Luke Skywalker is the son of Anakin Skywalker, Palps even tell Vader that the son of Skywalker must not become a Jedi. How did that happen though? From the new trilogy we know that Vader didn't know that Padme's twins have survived. Palpatine probably knew it but he surely didn't know that who are them. In the first episode of the original trilogy there were no signs that they knew it. So, it sound confusing to me how did they found it in the second episode. Was it that they feel a disturbance in the force for Luke, and combined with the events of him and Kenobi in the Star Destroyer made them link pieces together to know it, or did they made some research and found it. Or because Luke was a Skywalker they understood it?