User blog comment:Imperium Guy/British-German Union/@comment-4727448-20120924212422/@comment-4612798-20120926084139

Well Queen Victoria's first child Princess Victoria married Frederick III of Germany. If the UK had ever changed the law of succession to let females have the same rights as males when it comes to succession (like we're just getting around to doing now) Princess Victoria would have legally succeeded her mother. She would have reigned for about 8 months before dying, leaving her son Wilhelm II to inherit both Germany and the British Empire.

This would have obviously been a personal union rather than a full blown unification and whether parliament would ever have let even that happen is a whole other kettle of fish.