Princess Kate is expecting her second child.
"Their Royal Highnesses The Duke and Duchess of Cambridge are very pleased to announce that The Duchess of Cambridge is expecting their second child," said the official announcement Monday morning.
"The Queen and members of both families are delighted with the news."
The statement continued: "As with her first pregnancy, The Duchess is suffering from Hyperemesis Gravidarum. Her Royal Highness will no longer accompany The Duke of Cambridge on their planned engagement in Oxford today.
"The Duchess is being treated by doctors at Kensington Palace."
Kate and Prince William, both 32, welcomed son George in July 2013, and from the moment he was born, the third in line to the throne has captivated royal-watchers around the world.
From his first play date to learning how to walk, the chubby-cheeked toddler – whom William calls "a little rascal" – has kept his proud parents on their toes.
As for the arrival of his sibling, Kate is believed to be fewer than three months pregnant.
When she was carrying Prince George, she was admitted to the hospital suffering from the same illness before she was eight weeks along.
Monday's announcement came, in part, as a result of her having to pull out of that day's appearance in Oxford with William. The Palace is now reviewing her upcoming engagements, including her two-day visit to Malta scheduled for later this month.
She was also due to join William at brother-in-law Prince Harry's Invictus Games later this week.
Reporting by SIMON PERRY