Following the Wampa attack during the movie's opening scenes on Hoth; Leia, Han, and Chewie visit Luke in the infirmary. Leia is annoyed with Han, who insists she has feelings for him, so she kisses Luke to prove she doesn't. Presumably, the scene was simply meant to make Han jealous.
Ever since Return of the Jedi, Star Wars has reframed Luke and Leia's kiss as lacking real romantic intent - something Leia did solely to get a rise out of her real love interest, Han Solo.
Luke and Leia only discovered they were twins in Return of the Jedi despite being Force-sensitive. Could they have known earlier in Star Wars? Luke and Leia never sensed that they were twins until Return of the Jedi despite both being sensitive to the Force.
Following his nearly fatal encounter with a wampa on Hoth in The Empire Strikes Back, Luke Skywalker is rescued by Han Solo. In a medical center shortly after, Princess Leia checks on a recovering Luke, and in an effort to make Han jealous, she kisses the bedridden hero and walks away.
Darth Vader only learned he had a daughter in Return of the Jedi - but there's no evidence he realized she was Leia before his death and redemption. Darth Vader may have never known Princess Leia was his daughter in Star Wars and never cultivated a relationship with her, even when he was a Force ghost.
She figured out her mother's identity after Return of the Jedi, when she learned she was the daughter of Anakin Skywalker; it didn't take Leia long to connect the dots between Anakin and the senator of Naboo he had spent so much time with during the Clone Wars, who died under mysterious circumstances on the day Leia ...
In the post-2014 canon universe, the story that reveals Darth Vader discovering Luke Skywalker's identity (and thus the fact that the Death Star's destroyer is his son) is issue 6 of 2015's Star Wars comics by Marvel, which takes place sometime shortly after A New Hope.
In the 2015 film Star Wars: Episode VII – The Force Awakens, it is revealed that Han had a son named Ben with Leia. The family breaks apart following Ben's descent into the dark side as Kylo Ren, with Leia and Han separating. Luke is not revealed to have any children.
There is no implication or indication that Luke and Leia ever slept with one another, even before they knew they were siblings. If so, we must assume both of them would have had a “reaction” when they learnt the truth, but actually both of them seem remarkably little upset over it.
In between escaping the the trash compactor on the Death Star and returning to the Rebel Base on Yavin IV, Han Solo and Princess Leia did, in fact, sleep together during the events of Star Wars.
Alderaan's princess knew she had been adopted by Bail and Breha Organa after the Clone Wars, but she had no idea who her parents were. That was until Luke Skywalker told her the truth - that he was the son of Darth Vader, and that she was his sister.
This made Lucas realize that the prospect of Vader turning his sister to the dark side would make Luke lash out the way he did. Thus, the nascent concept of Luke and Leia being siblings provided a major emotional jolt for Vader and Skywalker's climactic fight.
Did Leia know Luke was her brother when she kissed him?
At the time, neither Luke nor Leia knew they were siblings, but this scene still feels a little odd given the context of their relationship as revealed in Return of the Jedi.
How did Luke Skywalker find out Leia was his sister?
Upon being told by Obi-Wan's force ghost that he had a sister, which Yoda had referred to as “another hope”, his insight through the Force gave him the name of Leia, which was immediately confirmed by Obi-Wan.
In hindsight, Luke had the luxury of carrying his father's real last name because he was a nobody hidden in the Outer Rim Territories. Leia, on the other, was adopted into a well-known and prominent family, hence why she was given the name Organa.
She assures him the conversation was about Luke learning that she is his sister, but the jealousy alone is enough for Leia to know that her love for Han is reciprocated. After avoiding dropping the L-bomb, Han finally tells Leia that he loves her when she saves him from some Stormtroopers.
A New Hope set up the idea of them being attracted to each other before The Empire Strikes Back planted the seeds for their familial connection, which Episode VI ultimately confirmed. The fact that making Leia and Luke related wasn't originally planned is well-known, but the retcon's background is more obscure.
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.
The twins, and eventually their younger brother Anakin, were sent to live at various safe havens, under the protection of Leia's handmaiden, Winter. In Jedi Search, the twins returned to Coruscant at age three and had many adventures there.
In the end, Rey takes the name Skywalker to show that she's the author of her future and can erase a past that was only hers by blood. With that in mind, she represented everything the name stood for, as Anakin, Leia and Luke all wanted more from their lives and chased it.
Returning to Dagobah to complete his training, an ailing Yoda told Luke the terrible truth that Vader was his father, Anakin Skywalker. Rather than destroy his father, Luke sought to bring him back into the light. At 900 years old, Yoda passed away, telling Luke that there was another Skywalker.
Instead of being in the life suit, Vader looks like an older Anakin who never received the devastating injuries, and Padmé and Luke (who struck down Palpatine) are by his side. It's during these visions Palpatine realizes Luke - who he only knew as the Rebel who destroyed the Death Star - is Anakin's son.
The two recognize Luke's similarities to Anakin and try to prevent him from sharing his father's fate, but they let him remain Luke Skywalker instead of having him go by Luke Lars out of respect for his grandmother, Shmi Skywalker.
