Responses
I think it's more than this, that's why not only him but many other lords rebels with him. Probably the price he is managing kingdom badly. Other thing they don't show him killing her ( her wounds are on the back mostly) so it is possible you are right and prince A. Is a killer.
They never show who kills her but this is an obvious "appearances can be deceiving" trope. Its a simple one but I dont mind it. I'm guessing the knight always rebels because he finds out the Prince is plotting to kill FL