I recently sat and thought (the most important part of weiting) about the ending of my yet unwritten 300k word grimdark historicak epic set in the thirty year war where in the last chapter it turns out that all the characters are aliens from the planet Zeist (a subtle nod to my favorite piece of writing)

But when I shared this with my friend (after swearing him to secrecy and threatening to break his playstation (4 lol) if he stole my ideas) he told me that I can't just put a twist like that at the end of my book because it will feel really out of nowhere and dumb????

He's wrong right? Right??? Please tell me what you think (unless you disagree with me do not comment if you don't think it's a good idea >:(

P.S. don't steal my idea or I will slap you with legal

P.p.s I'm an author btw