WARNING: This review likely contains a ton of grammatical and spelling errors that I am too lazy to fix. There is also a lot of capital letter excitement. Proceed at your own peril.
Wow. Just... wow. This ending was everything I expected and so, so much more. There's intrigue and war and humor (yeah, maybe I should change the order of this list) and villain romance and compelling characters and sibling dynamics and twisting morality and magic and did I mention VILLAIN ROMANCE? Anyone who has read my reviews knows that I've been a fan of this series since the beginning. They're easy to read, fast-paced, and all-together fun. And I know what you may be thinking: how can a series about a human sacrifice turned heir to the throne turned totally-not-evil queen be fun? Well, the books are written conversationally, with modern dialogue and ideas despite the fantastical setting. Even in the middle of a battle scene, there would be something to smile or squeal about, and while Kasta/Zahru were sort of evil, they didn't cross the line into war crimes level evil.
There isn't a ton I can say without spoiling literally this entire series, so I'm going to keep things as vague as physically possible going forward (you've been forewarned). Zahru is a wonderful main character. From the start of this series, her powers come from kindness. Not swords or magic or position, but from the way she helps other people selflessly. Obviously, things have changed from book one, but I liked how her friends never let her forget who she was and why she wanted to change the world. Kasta (ahh, how to say any of this without spoilers?)... changed. But despite developing as a person, it was still easy to see who he had once been, and his past wasn't erased in favor of a cheap redemption arc.
The side cast of characters was part of what made this book so great. Unlike some other squads in fantasy, they don't let Zahru become the person she doesn't want to be, and are supportive whilst also maintaining a backbone (a rareity in YA fiction for some reason). The shifting dynamics within the group created tension without unnecessary drama, and all made sense. As for the side romances, I thought they were a perfect solution to what otherwise could have been a very tiresome love triangle.
The writing was great (to the surprise of absolutely no one), maintaining a cinematic feel while staying ground. Did I mention that this trilogy needs to be turned into a TV show? No? Well, it should become a TV show. Preferably one that actually stays true to the books and doesn't ignore character and plot development (I'm looking at you "Shadowhunters"). The plot sped ahead, and I found myself unable to put the book down. There wasn't a dull moment, and breaks from the action were filled with what I like to call necessary fluff and angsty let's-pretend-I'm-not-in-love-with-my-enemy moments. To end this chaotic review, I must remind you that The Sweetest Betrayal contains a I'll-be-the-villain-for-you romance. Need I say more?