favorite plot twist/surprise reveal?

one of the defining characteristics of this series is its plot twists, whether that comes in the form of an unreliable narrator, outsider point of view, or some other dramatic form of withholding details until the last minute. a few people have called this out as one of their favorite characteristics of the books, so:

which plot twist or surprise reveal of the books is your favorite? this can be the most shocking, the most emotionally impactful, or your favorite on any other metric. let us know your answer (and why) in the comments! (as always, you can have more than one!)