And? So? Who cares? Any given random person who lived in the 12th century who has descendants down to the present likely has many millions if not hundreds of millions of descendants. The majority of people of English ancestry are almost certain to be descended from the Angevin and Plantagenet kings. The number of ancestors you have doubles with every generation; at a certain point you have more potential ancestors than people who were alive, and thus you must necessarily be a descendant of most of the people in a given population who left descendants down to the present. 29 generations ago one has over 546 million potential ancestors; the population of England in the year 1300 was only around 3 million (and declined by nearly half thanks to the Black Death at mid-century, so a significant percentage of that three million have no descendants). Considering that, it would be far stranger (approaching mathematical impossibility) if, being of mostly English ancestry, you were not descended from Henry I or John Lackland.