Anybody who had children more than a few hundred years ago likely has millions of descendants today

This is true. It is also true that Edward III was likely the most prolific King in England as 80% of all English people in England descend from him. So, it is easy to say that 80% of English people are descended from Royalty just from this one truth regarding King Edward III of England.

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Genealogist: Almost Everyone on Earth Descended From Royalty ...

www.foxnews.com/.../genealogist-almost-everyone-on-earth-descended-from-royalty....

Jul 5, 2006 - Genealogist: Almost Everyone on Earth Descended From Royalty. Actress Brooke Shields has a pretty impressive pedigree — hanging from her family tree are Catherine de Medici and Lucrezia Borgia, Charlemagne and El Cid, William the Conquerer and King Harold, vanquished by William at the Battle of Hastings.
It works the other way, too. Anybody who had children more than a few hundred years ago is likely to have millions of descendants today, and quite a few famous ones.
Take King Edward III, who ruled England during the 14th century and had nine children who survived to adulthood.
Among his documented descendants are presidents (George Washington, Thomas Jefferson, John Quincy Adams, Zachary Taylor, both Roosevelts), authors (Jane Austen, Lord Byron, Alfred Lord Tennyson, Elizabeth Barrett Browning), generals (Robert E. Lee), scientists (Charles Darwin) and actors (Humphrey Bogart, Audrey Hepburn, Brooke Shields).
Some experts estimate that 80 percent of England's present population descends from Edward III.