You find out Luke and Leia are siblings in Star Wars: Episode VI – Return of the Jedi during two key moments.

On-screen reveal in the movie

  • The audience gets the explicit confirmation on Endor, when Luke tells Leia that Darth Vader is his father and that she is his sister, saying she is the “other” Skywalker Yoda spoke of.
  • Leia responds with “I know. Somehow, I’ve always known,” which retroactively reframes their bond in the earlier films as a sibling connection rather than just a romance subplot.

How Luke learns the truth

  • After Yoda dies, Luke speaks with Obi-Wan’s spirit, who confirms that Vader is his father and that Luke has a twin sister.
  • Luke then realizes that sister is Leia, which leads directly to the emotional scene on Endor where he shares this with her before confronting Vader and the Emperor.

Behind-the-scenes context

  • Early planning for the original trilogy had Luke having a sister somewhere else in the galaxy, not originally intended to be Leia.
  • When the story was condensed to end with Return of the Jedi , George Lucas decided to make Leia the sister to tie up the “there is another” line from The Empire Strikes Back and give Luke a stronger emotional trigger in his final duel with Vader.

TL;DR:
Luke and Leia being siblings is revealed in Return of the Jedi —Luke learns it from Obi-Wan after Yoda’s death, and the audience gets the emotional confirmation when he tells Leia on Endor.

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