Along with Monday's joyous announcement that Kate Middleton is pregnant came news from the palace that the Duchess is in the hospital with severe morning sickness.
Hyperemesis gravidarum is a rare, acute morning sickness resulting in weight loss; it accounts for about 2 percent of all morning sickness, according to doctors.
The condition is sometimes associated with women having twins, experts say.
Hyperemesis gravidarum is believed to be caused by higher levels of the pregnancy hormone, hCG; Extra hCG can often be brought on by carrying more than one fetus.
In other words, it could be a sign that Kate Middleton is pregnant with twins.
Although there's very little data to go on, one study showed that women carrying twins had a 7.5 percent higher risk of experiencing the acute morning sickness.
In any case, it poses little danger to the tiny heir(s), doctors said.
Women diagnosed with hyperemesis gravidarum often lose 5 percent of their pre-pregnancy weight, or 10 pounds, but it is not indicative of troubling complications.
It's traditionally thought that nausea and vomiting is a sign of a healthy pregnancy, even. That's not to say it isn't brutal for the mother-to-be to live through.
Dr. Nancy Cossler, an OB/GYN at University Hospitals in Ohio, said the condition does not cause loss of pregnancy or birth defects, but is torture to endure.
"The biggest problem with this is how it interferes with your life," Cossler said.
"Constantly feeling sick and puking is obviously unpleasant and difficult."
The extreme morning sickness is usually diagnosed about nine weeks into the pregnancy, and in most cases resolves itself by 16-20 weeks, according to experts.
Kate Middleton's pregnancy is likely around the 12-week mark at this time.
"As the pregnancy is in its very early stages, Her Royal Highness is expected to stay in hospital for several days and will require a period of rest thereafter," St. James Palace said.
Prince William is at the hospital with Middleton, according to news reports.
If she were carrying twins, the first-born would be the heir to the throne, regardless of gender. One can imagine the twins fighting in the whom over that distinction!