User blog comment:Imperium Guy/British-German Union/@comment-4727448-20120924212422/@comment-32656-20120926101404

...And if they had changed the succession laws, or the younger Victoria had come to the throne by other circumstances, she would not have married Frederick. Her mother/Parliament would have ensured she married someone else that would have meant they could not get entangled in continental politics.

It would take a scenario like that timeline for Wilhelm to become King of GB - and even it is a bit of a stretch, quite frankly.