SilverWook said:
If you’ve ever seen the documentary Star Wars To Jedi:The Making Of A Saga, Lucas implies they made Leia the other at the last moment. When they came to shoot the throne room scenes, they still had not figured out what Vader should say to make Luke fight him.
The irony is that if Lucas had allowed the ‘noble death’ of Han Solo, he would’ve had the answer to the ‘why does Luke snap’ conundrum. Vader/Palpatine could have been offering to halt the battle if Luke were to agree to turn (an actual temptation as opposed to simply making Luke mad) before Luke suddenly senses Han’s death through the Force. Luke kicks Vader’s butt and no-one has to be anyone’s shoehorned sister!