Forum:KB:Did Vader truly know before ESB

Don't know if this had been brought up before, but I must know based on the Anakin Skywalker page...
 * Pre-Hoth: The pilot was a young man, and wielded a blue lightsaber. Vader looked upon him as an untrained child who had no right to the weapon of the Jedi. The young man in reality was Vader's long lost son—Luke Skywalker. Although this family relation was unknown to both father and son.
 * Hoth: Secretly, Vader planned to find Luke Skywalker, whom he knew was his son and who he wanted to turn into his apprentice to destroy the Emperor.
 * Post-Hoth: Once the Executor was clear of the asteroid field so that the transmission would be clear, Vader contacted his Master. Sidious told him that he had sensed a new threat in the Force: the Rebel pilot who had destroyed the Death Star. Vader acted surprised when Sidious told him that the boy was the child of Anakin Skywalker.

Taking from all I could find on the current version of the Anakin Skywalker article. Out of curiosity, how would Vader have known Luke was his son before Empire? Of course we know he referred to him as "Skywalker" up until the scene with the Emperor, but no where (so far) is the evidence that Vader learned of Luke's parentage before "Search your feelings, Lord Vader...". So is the information fake or has the story not come out yet in the current canon we know now, or simply the explanation hasn't been posted? Any answer or clarification would greatly be appreciated. 71.28.19.145 05:36, November 1, 2015 (UTC)