Just as with her other pregnancies, she's suffering from morning sickness.
While rumors had been flying that the Duchess of Cambridge may have been pregnant ever since she was given a gift for infants in Poland (she joked that she and Prince William may need to have more babies), the Palace confirmed the pregnancy Monday morning because Kate had to cancel an appearance due to her morning sickness.
"Their Royal Highnesses The Duke and Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting their third child," reads the statement, which the Palace tweeted out Monday morning. "The Queen and members of both families are delighted with the news. As with her previous two pregnancies, the Duchess is suffering from Hyperemesis Gravidarum. Her Royal Highness will no longer carry out her planned engagement at the Hornsey Road Children's Centre in London today."
This isn't the first time Kate Middleton has dealt with extreme morning sickness during pregnancy. The Duchess of Cambridge also experienced Hyperemesis Gravidarum, a pregnancy complication also called HG, when she was expecting George, now 4, and Charlotte, now 2. Because the condition is a very severe form of morning sickness, she had to announce those pregnancies earlier than planned.
"The cause of nausea and vomiting during pregnancy is believed to be rapidly rising blood levels of a hormone called HCG (human chorionic gonadotropin), which is released by the placenta," according to the CDC, which notes that intensive treatment may be needed for some women.
According to the Palace's statement, The Duchess is getting the medication care she needs at Kensington Palace.
There's no word yet on how far along Kate Middleton is in her pregnancy.
When Prince Harry was asked about the news before heading into a meeting in Manchester, he said "Fantastic, great, very, very happy for them," according to a video tweeted by Daily Express reporter Richard Palmer.
Congratulations, Kate and William!