If you don't believe that Papyrus is the Knight, then reread this.
https://toby.fangamer.com/interviews/nine/

>AND THAT SEVEN WAS JUST A MISLED ANTIHERO!?
>Umm... If Seven loved Five, maybe they were...
>... just doing what they... felt like they had to...

>if seven is a misled antihero...
>is negative seven a villain who thinks he's good?

>WHAT!? I'M THE VILLAIN!?
>hmm. maybe you seem like an enemy,
>but you're actually a good guy.
>WHAT? WHY WOULD I EVER BE AN ENEMY?

Papyrus is the Knight, who is being misled into believing that what he's doing is right.