That Arthur kid has some serious issues... normal people, especially nobles would know about manner. That you don't barge in into someone's room and disturb their sleep. Even young nobles know and he's 19??
And this was a woman he's confronting. A wife, a duchess. And yet he dared to do that? Thank goodness it's Astina, if it's other nobles he would be in so much trouble already, might loose a life not just tongue.
And yes my lady please cut his tongue. My guess it could save his life in the future if we look at how he's currently behaving.