Are you talking about Smythin (
https://forums.larian.com/ubbthreads.php?ubb=showflat&Number=836909)?
He’s not new, but easy to miss as depending on how you go about dealing with the sanctum he can get shoved in the pit before you get close enough to see him.
As per my linked post, he didn’t die immediately in my paladin playthrough though not because I did anything, and then he got killed by goblins but there was no impact on my oath (of Devotion, in my case). The oath breaking logic is extremely wobbly at the moment, though. I’m sure Larian are planning on working on this anyway, but it couldn’t hurt for you to submit a bug report outlining specifically what you did with respect to Smythin that resulted in a broken oath.
