Claudia Gray's novel Bloodline established that Leia struggled with the knowledge that Darth Vader was her father, as her memories of the Dark Lord of the Sith were the stuff of nightmares.
Vader discovers Leia is his daughter because of Luke.
Luke had only recently discovered the two were siblings and, even more recently, had revealed their connection to the princess. Vader likely sensed their emotional bond through the Force when speaking with his son.
Darth Vader's true identity as Anakin Skywalker was a highly guarded secret, known only to a select few individuals including Palpatine, Obi-Wan Kenobi, Luke, Han, Leia, R2-D2, C-3PO, Master Yoda, Bail Organa, Ahsoka Tano, Darth Maul, Grand Moff Tarkin, Grand Admiral Thrawn, Jocasta Nu, Ferren Barr, Verla, Reva, ...
How did Leia react when she found out Vader was her father?
Luke, Leia, and Han are on Endor. First, Luke tells her Vader is his father. Her first reaction is one of slight revulsion, perhaps even of him. She gets a very concerned look on her face.
Darth Vader didn't learn he had a daughter until Return of the Jedi, when he stood before Emperor Palpatine. The Emperor's power probed Luke's mind, attempting to goad him to fall to the dark side, and he discovered Leia's existence. "Sister," the Emperor taunted.
Leia and Han had three children, and they named their youngest son Anakin after Anakin Skywalker, Leia's biological father. Since Luke was the twin to spend more time with Obi-Wan in the old canon, it made sense that he, not Leia, was the one to honor Obi-Wan when naming his child.
Yes. In Truce at Bakura, Anakin's ghost appeared to Leia, begging for her forgiveness. She rejected him. Only by Tatooine Ghost did she start to come around to the father underneath the suit, just in time for her to finally have kids in the Thrawn Trilogy.
Leia was not using the Force or was currently Force-sensitive during her confrontation with Vader. She began training as a Jedi years later. All these reasons prove my point: Vader didn't know Leia was his daughter, and felt no presence of the Force in her, as she was not currently strong with the Force.
He eventually became so desperate to find a way to prevent Padmé from dying that his fear was ultimately the main reason that led to his fall to the dark side. Vader screaming for the loss of Padmé. Even as a Sith Lord, Anakin still loved Padmé very much, but felt great guilt for his actions against her.
R2-D2 was present when Padmé gave birth to Leia and Luke, so he knew Luke was Anakin's son – but what he didn't know was that Anakin became Darth Vader. In addition to that, Anakin's fall was surely a painful event in R2-D2's life, one that he definitely wouldn't like to remember or even talk about.
Here, Vader employs mind-altering drugs and subliminal suggestion in his sessions with the princess, which make Leia believe that her skin is on fire and her flesh being torn apart, causing the same reaction the real thing would. An altered version was presented in the current Star Wars canon.
She was not genetic Organa but still, she is rightful Organa. So yes, Palpatine knew that Leia is daughter of Anakin as well as the fact that Ben is the son of Leia and Han.
Finally, Rey is Kylo Ren's aunt through Anakin Skywalker. This means that Kylo and Rey's romance is just as genetically awkward as Luke and Leia's kiss on Hoth was. Granted, neither pair knew they were related at the time, but that's no excuse.
It is well worth remembering that, as far as Vader knew at the end of "Revenge of the Sith," he had killed Padme and his child did not survive. It is also very important to point out that he had no idea Padme was pregnant with twins. This will come into play as it relates to the Leia situation.
Han Solo marries Princess Leia and they have three children: twins named Jacen and Jaina, and a younger son named Anakin. Luke reestablishes the Jedi Order, marries a non-movie (but fan favorite) redheaded Force-wielder named Mara Jade, and they have a son, Ben Skywalker (named in honor of Obi-Wan “Ben” Kenobi).
Darth Vader acts like he doesn't even know C-3PO or R2D2. They were with him since he was a child. He did everything he could to forget his past. Also, his plating had been replaced many times, and protocol droids all look very similar.
Luke and Leia never sensed that they were twins until Return of the Jedi despite both being sensitive to the Force. Anakin Skywalker's twin children are the original Star Wars trilogy's driving force, having been separated after Padme's death.
