No, it wasn’t just the audiences and actors who were kept in the dark about the larger plans for Star Wars at first. John Williams also had no idea there would be a second movie and wasn’t stopped by George Lucas when he wrote Luke and Leia’s theme in A New Hope as a love theme.
However, unlike Han Solo shooting Greedo first, this wasn’t changed in future releases because the music was too much of a Force-powered banger from the maestro (like the entire original score). Thank the Maker for that.
The surprising revelation comes from Variety’s latest piece on John Williams’ career and many achievements, among which is scoring the entirety of the nine-movie Skywalker Saga plus some key themes used in recent spinoffs. Williams’ sole “blip” while scoring the first movie wasn’t his fault, as he explained: “I mistakenly wrote a love theme for Princess Leia and Luke Skywalker. I learned later that they were brother and sister, so it was an incestuous idea to have a love theme for them. But George never told us there was going to be a second film!”