I have a friend who does geneology who says her line includes kings, queens, prime ministers, bishops,....and horse thiefs, slave traders and murderers! Don't we all!!!
If your lines run into the Bristish Isles and generally Western Europe, you will probably run into royalty, mostly because it was in general the upper classes that survived the plagues and wars, and there is a LOT of inbreeding. Luckily, the royal lines are well documented.