DARTH VADER IS LUKE'S FATHER!? DUDE, WTF, SPOILER WARNING!
That said, I'm not sure the "revelation" that what is rather clearly a Daemon of Tzeentch is untrustyworthy is some massive plot twist and spoiler. It's honestly expected even in-character!
Likewise, it says he's a lying douchebag right there in his stat block! Which is free to look at on the internet for anyone who cares, now, even without this post. The fact that his name echoes what he is in French is a fun little tidbit, not some well-kept secret.
And, lastly, any time he shows up to mess with the players, he's unlikely to give his real name, since he likes impersonating other things and beings to lead people astray.
All in all, I think you are overreacting.