Kate Middleton and Prince William are expecting their third child together.

Kate Middleton Pregnancy News

The Duke and Duchess of Cambridge are already parents to 4-year-old Prince George and 2-year-old Princess Charlotte.

“Their Royal Highnesses The Duke and Duchess of Cambridge are very pleased to announce that The Duchess of Cambridge is expecting their third child,” a statement from Kensington Palace released Monday morning said.

The statement also added that Middleton, 35, is suffering from Hyperemesis Gravidarum — a condition primarily characterized by acute morning sickness — which she also endured throughout her first two pregnancies.

Middleton canceled a scheduled appearance Monday morning.

“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,” the statement said.

“The Duchess is being cared for at Kensington Palace.”

Middleton is believed to be less than three months pregnant. However, Kensington Palace announced the news early due to her illness.

“Hyperemesis gravidarum is not your typical morning sickness. The vomiting is so frequent (usually more than 3-4 times a day) and severe that it can leave you dehydrated, deficient in important nutrients, and unable to maintain a healthy weight (losing more than 10 pounds).”

Prince William told dignitaries at a policing and mental health conference in Oxford on Monday that he and Middleton had gotten the chance to “start celebrating this week” after “it was a bit anxious to start with.” The Duke also confessed that “there’s not much sleep going on at the moment,” according to Time Magazine.

Following the child’s birth, Prince Harry will drop to sixth in line to the throne.

During an appearance Monday, Harry told reporters the news is” “fantastic, great. Very, very happy for them.” Asked about Kate he added, “I haven’t seen her for a while but I think I she’s okay.”

In other news concerning the English royal family, Prince George is scheduled to begin school at Thomas’s Battersea on Thursday.

The birth of the third royal child could make history: if it is a boy, he will not displace Charlotte in the line of succession, thanks to a measure that passed just after Will and Kate’s 2011 wedding. Before this law was passed, a younger son could usurp his older sister’s place with regards to inheriting the throne.