Yes, beware, ANY powerful low loyalty general could decide to lead a civil war -- this is why you get warning scrolls about having a lot of disloyal generals. High command/low loyalty is a combination to be wary of. Give him a title, an office, or a princess to keep his eyes off the throne

Other than that keep him in your king's stack, but that is a waste of his command ability, although you should be able to move him out on his own once your king has gained extra influence or loyalty-boosting virtues ("builder" line etc). And try not to be caught unprepared when your old king dies, as your new one will not have the same loyalty factors (unless you carefully groom your heir apparent, of course )