Immediately after I saw Force Awakens, I told my friend Episode 9 would have Kylo Ren turn good and sacrifice himself to save Rey; although I expected him to die by fiery explosion after sending her off in an escape pod.
I don’t know if these other two count because who was really surprised?
Boba Fett being resurrected as a grizzled anti-hero. Called that pretty much when the Madalorian was announced.
Senator Palpatine alter ego being Darth Sidious. 9 year old me deciphered this when I saw his name and picture on a pog when Episode 1 was released.