Quest target has yielded. Should I kill him anyway?

My lord has sent me to kill a Jaguarman - I spent a little while wandering around the hamlet where he was last seen, only to find out that he's ruling over it as lord.

So, I did what any sensible person would do, and stabbed him. A lot. His hearthperson/guard doesn't seem to mind, but now that he's on the floor and bleeding, he's surrendered, and the game has asked if I'm really sure I want to attack someone who's yielded.

What are the consequences of killing or sparing him? Will killing him anger his hamlet? Will sparing him anger my lord?