Kensington Palace says Prince William and his wife, the Duchess of Cambridge, are expecting their third child.
The announcement released in a statement Mondays says the queen is delighted by the news.
Officials say Prince William's wife, the former Kate Middleton, is suffering from Hyperemesis Gravidarum, a form of severe morning sickness, and will not carry out her engagements Monday.
William and Kate already have two children, Prince George and Princess Charlotte.