isn't it illegal to bomb a head of state?
i'd look the other way, just this time. call it an exception.
but, what legitimate grounds does the saudi monarchy have to call themselves heads of state? there's no election, no constitution - not even a pretense of democracy. the closest thing they have is a kind of "right of kings" type argument, which has been debunked as nonsense since the end of the dark ages.
so, i'd have a hard time calling mbs a "legitimate head of state"; he just isn't. he's an aristocrat that assumed power, and there's no legitimacy in that.
that's putting aside the fact, of course, that he's only an acting head of state just right now.