This is certainly something that isn't focused on in the game. I think a lot of what has been said already is very plausible. As it stands, we have no real evidence that Queen Brahne was all that kind before the King's death anyway, it is possible that that was to some extent a facade.

Human history has shown many a time that absolute power corrupts absolutely - or at least very often. People in such positions often only see their own lives and ambitions as having any meaning and therefore commit horrible crimes as a result.