The Duke and Duchess of Cambridge have said they are "very pleased" to reveal they are expecting their third child.
In a statement, Kensington Palace said: "The Queen and members of both families are delighted with the news."
The statement also said the duchess had to cancel planned engagements on Monday because – as with her previous pregnancies – she is suffering from severe morning sickness, or hyperemesis gravidarum.
She is receiving treatment at home, the palace added.