If Prince William and Kate Middleton, the Duchess of Cambridge, have twins, some doctor could end up determining which one gets to be the heir.

Kate has a condition called hyperemesis gravadarum -- also known as acute morning sickness -- which can indicate twins. Plus there have been twins in each of the royal couple's families, but none has been close to the throne.

"It doesn't really change anything," royalty expert and ABC contributor Victoria Arbiter told E! News (her father was a press secretary to Queen Elizabeth II). "All it really means in one fell swoop we would have provided the nation with an heir and a spare. So job done really!"

Not if you're the spare.

E News! said that, according to British law, the firstborn of an heir to the throne gets the big crown, regardless of gender. (The law used to favor boys, but changed last year.)

Here's where it gets fun.

Whichever kid falls out first, wins ... UNLESS Kate needs a cesarean section. If so, her doctor could end up deciding the royal succession by determining which child comes out first. Or the position of the kids at the time of delivery could make the determination. Or any number of other factors could decide this thing.

This would make a good movie.

"Any doctor knows their No. 1 concern is the health and well being of the mother and the baby," Arbiter says. "They wouldn't be picking which baby to pull out first. They are picking the baby that needs to come out first in order to get the other baby out. So, it doesn't change things."

Uh-huh. Until the Masons, CIA and Illuminati get involved.

Contact Tony Hicks at thicks@bayareanewsgroup.com or on Facebook at www.facebook.com/BayAreaNewsGroup.TonyHicks.