The Duke and Duchess of Cambridge are expecting their third child, Kensington Palace has announced.

The Duchess is less than 12 weeks pregnant, but was compelled to bring forward the announcement after being too ill to make an appearance at a planned event today. 

In a statement, the palace said the Duchess was suffering from severe morning sickness, as she did with her previous pregnancies.

Prince Harry he was feeling “fantastic” about becoming an uncle for the third time, adding: “Great. Very very happy.”

When asked how his sister-in-law was getting on, he told reporters: “I haven’t seen her for a while but I think she’s ok.”

The Prince of Wales, the new baby’s grandfather-to-be, is “delighted” with the news, Clarence House said. 

A Kensington Palace  statement said: “Their Royal Highnesses the Duke and Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting their third child.

“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.

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

Just a few weeks ago, the Duchess hinted that a third baby was on the cards. During a visit to Poland, she was presented with a cuddly toy designed for newborns. She turned to the Duke and laughed: “We will just have to have more babies.”

The Duchess is one of three children, and enjoyed a happy childhood with her siblings, Pippa and James.

The new baby will be a sibling for George, who turned four in July, and Charlotte, who celebrated her second birthday in May.

The Duchess’s last public engagement was a tour of Kensington Palace’s White Garden last week, to mark the anniversary of the death of Diana, Princess of Wales.

Wearing a floral dress and sheltering beneath an umbrella, she showed no outward sign of feeling unwell.

In July, when she was in the early stages of pregnancy, the Duchess undertook a tour of Poland and Germany, participating in a rowing race. Afterwards she was handed a stein of local beer to toast the rowers.

The news was announced as the royal couple were preparing to send their eldest child, Prince George, off to school for the first time.

They have chosen a fee-paying independent school in a south London borough for their four-year-old son.

Thomas’s Battersea will welcome the young prince and his parents on Thursday.

George’s first day at school will also mark a new chapter for the Cambridges as they are now mainly based in their Kensington Palace apartment rather than their Norfolk home Anmer Hall.

William, who quit his job as a pilot for the East Anglian Air Ambulance in July to become a full-time royal, is also due to attend the National Mental Health and Policing Conference in Oxford on Tuesday.

The couple’s third child will be born fifth in line to the throne, bumping uncle Harry out of the top five and into sixth place.

The Prince of Wales is first in line, followed by William, Prince George and the couple’s daughter Princess Charlotte, who is two.

William Hill is offering odds of 33/1 that the Duchess is pregnant with twins. Alice is the bookmakers’ favoured name if the baby is a girl, followed by Elizabeth and Victoria. For a baby, the shortest odds are on James, Arthur and Phillip.