Seems a bit like the Norman invasion.
Good analogy, imho. There are reenactors in Britain who regard the Battle of Hastings (a.k.a. the Battle of Senlac) as the death knell of England.
The British dynastic lines do indeed run back to Alfred the Great (many people, including this writer, are descended from A the G, most of us more than once), but a number of the British monarchs were foreign, didn't speak whatever was the current spoken English, and spent their reigns busting the asses of the common folk, as well as their dynastic rivals.