The Duke and Duchess of Cambridge are expecting their third child.
A statement said the royal couple and the Queen are "delighted with the news."
However Kate Middleton is suffering with Hyperemesis Gravidarum, which she also went through in her two previous pregancies with George and Charlottte.
The condition causes severe nausea and vomiting.
This means she will not be visiting Hornset Road Children's Centre in London today (September 4) as originally planned, and is instead staying at Kensington Palace to be cared for.
More to follow