Leia wasn’t going to be Luke’s sister

The biggest twist in 'Return of the Jedi' is that Luke and Leia are revealed to be siblings, but that wasn't always the case.

George Lucas initially planned on making a sequel trilogy that would introduce Luke's sister, but after becoming exhausted from the franchise, the visionary opted to instead tie up all loose ends in 'Return of the Jedi' and make the pair twins.

He had also struggled to come up with a reason for Luke to lose control and become enraged during his climactic fight with Darth Vader, and eventually decided the suggestion of his sister falling to the Dark Side worked perfectly.

Reflecting on the decision, George said: "In the process of evolving the script and evolving the importance of Leia as the sister, it was sitting right there in front of my face, and it became obvious that turning her to the dark side would be the thing that would set Luke off again."