Given the following reasoning and answer, what was the question? To answer the above question, the relevant sentence is: In Return of the Jedi (1983), Leia leads the operation to rescue Han from the crime lord Jabba the Hutt, and is revealed to be Vader's daughter and the twin sister of Luke Skywalker.
The answer: In Return of the Jedi ( 1983 )
The question Passage: Princess Leia Organa of Alderaan (also Senator Leia Organa or General Leia Organa) is a fictional character in the Star Wars franchise, portrayed in films by Carrie Fisher. Introduced in the original Star Wars film in 1977, Leia is princess of the planet Alderaan, a member of the Imperial Senate and an agent of the Rebel Alliance. She thwarts the sinister Sith Lord Darth Vader and helps bring about the destruction of the Empire's cataclysmic superweapon, the Death Star. In The Empire Strikes Back (1980), Leia commands a Rebel base and evades Vader as she falls in love with the smuggler, Han Solo. In Return of the Jedi (1983), Leia leads the operation to rescue Han from the crime lord Jabba the Hutt, and is revealed to be Vader's daughter and the twin sister of Luke Skywalker. The prequel film Revenge of the Sith (2005) establishes that the twins' mother is Senator (and former queen) Padme Amidala of Naboo, who dies after childbirth. Leia is adopted by Senator Bail and Queen Breha Organa of Alderaan. In The Force Awakens (2015) and The Last Jedi (2017), Leia is the founder and General of the Resistance against the First Order. She and Han have a son named Ben, who adopted the name Kylo Ren after turning to the dark side of the Force.

Question: Based on this passage, when is it revealed that luke and leia are siblings?