And, according to medical experts, the 30-year-old royal's next few months may continue to be rather unpleasant.
Though morning sickness is a common enough affliction, what Middleton is suffering from—a more acute form of the condition with the Harry Potter-esque name hyperemesis gravidarum—is not your average, throw-up-and-go-about-your-day business.
HG is "nothing like run-of-the-mill morning sickness," Dr. Marlena Fejzo, an obstetrics researcher at the University of California, Los Angeles, and a leading expert on the condition, tells E! News. "We have women who have vomited so hard that they've blown out their eardrums or their ribs fracture. They're unable to eat much."
"She has to stay hydrated and try to keep something down every day," she says of the expectant royal. "They need to be careful that she's able to keep vitamins down."
Up to 20 percent of women in the United States who are hospitalized with HG end up on a feeding tube, Fejzo says, noting that the number in the United Kingdom is much lower, but she wouldn't be surprised if Middleton is getting intravenous fluids at home.
Though she was released from the hospital last Thursday, Middleton has cleared her calendar for the foreseeable future, including an outing to the London premiere of The Hobbit tomorrow, after suffering a relapse of symptoms.
So, what can her family do to make her more comfortable while she rides this out?
First of all, Will may have to ditch the aftershave and find a sitter for their puppy Lupo.
"People say that you could use a woman with HG as a police dog," Fejzo says. "Their sense of smell becomes extremely, extremely strong. The different smells and different people's odors can cause nausea to be worse.
"A lot of people are sensitive to shampoo, sensitive to animals, definitely smells of cooking. Kate should stay away from food being cooked, stay far away from kitchens and the market. People shouldn't wear perfume or cologne around her."
"A lot of women with HG have a fan near them," she adds. "They feel hot, just like when you have stomach flu. They need fresh air. Their windows can be kept open to keep the air fresh and cold." (England in the winter? Done and done.)
But though its symptoms and possible consequences are more severe, hyperemesis gravidarum—like morning sickness—is considered to be hormone related.
And who produces female hormones? That's right. Girls. Or, perhaps in this case, little princesses.
Fejzo acknowledges that there "is a slight increase" in the rate of female births among women who suffer from HG. "We do find that women carrying female fetuses tend to be hospitalized longer than when they have males."
Well, we just hope that Kate feels better soon and whoever's in there stays healthy!