Luke and Leia learn they are siblings in Return of the Jedi , during their private conversation on Endor, shortly before the final battle.

In-universe timeline

  • Leia’s realization : Luke tells Leia on Endor that Darth Vader is his father and that she is his sister, revealing they are twins separated at birth.
  • Luke’s confirmation : Luke fully understands the truth after Yoda’s death on Dagobah, when Obi-Wan’s spirit confirms that Leia is his twin sister.

Before that reveal

  • In A New Hope and The Empire Strikes Back , neither of them knows they are related, which is why their dynamic often leans romantic rather than familial.
  • The famous kiss in The Empire Strikes Back happens while both still believe they are just friends and potential love interests, adding to the later awkwardness once the sibling twist is revealed.

TL;DR: Luke learns Leia is his sister on Dagobah (confirmed by Obi-Wan), and Leia learns it directly from Luke on Endor in Return of the Jedi.

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