I notice you didn’t say it wasn’t true. But at least he was British.
And the present day Royals ARE Brits!
Do you really want to go all the way back in history to find an 100% indigenous Brit king? There wasn't one, for all of England!
William the Conqueror was a Norman; part French, part Viking and he was the first king who was king of the whole nation and not just parts of it.
And well before the Germans came in, there had been intermarriage spouses from France and other nations.
James I was a Scot, for instance.