Thanks, but I do think that he was always kinda villainish - not evil, but he sailed in desperate to marry into power to get away from his shit life situation, no matter what it took. And he was clearly a bit amoral, maybe as a result of having been brought up in a brutal loveless family, if he thought that playing with someone's heart and pretending to like them was perfectly fine if it got him where he wanted.
But I don't think he planned to kill anyone from the start, he just wanted to marry into power whatever it took. Turns out it takes a coup, maybe murder, okay. Unfortunate but okay.
And then on top of that he had the personal resentment towards Anna that had accumulated during their courtship (despite his initial attraction to her), which he finally let out once it was clear Anna's as good as dead anyway and nothing can be done, so might as well let his real feelings out since she won't live long with the knowledge.
So it kinda makes sense, but I do wish they'd animated it a bit clearer.