I apologize, you may be right. I just loaded up my game to check it out. I thought some of my descendents had the royalty trait and they actually don't. It looks like the number is somewhere around 10 people.
I had missed the update on the royalty bonus in the change log, so I was very surprissed to see my cities jump from +4 to +44 (and my home city to +99) and it definitely didn't seem right. I ended up with three fairly new cities hit metropolis level in about 20 turns which seemed rather fast.