The Duke and Duchess of Cambridge are expecting their third child, Kensington Palace has announced.
The Queen and both families are said to be "delighted with the news".
As with her previous two pregnancies, the duchess, 35, is suffering from hyperemesis gravidarum, or severe morning sickness.
Catherine is being cared for at Kensington Palace, the statement said.
The child will be the Queen's sixth great-grandchild.