So the Beast's Ruler didn't really intended to kill his wife...
Well, for a leader, he would need to use a facade,
but that led to forcing his wife to take the blame (which his wife did on his behalf for her love for him) just to alleviate or stop the factions fight between themselves.
Yeah, tragic if that's the case.
P.S. I didn't read the source, so this is just me reading between the lines as always. lmao
(I added ISPOILER just in case)
Btw, looks like the Beast Ruler really loved his wife, so he
forcefully? tried to take the siblings away because he is worried, terribly.