The Duke and Duchess of Cambridge have announced they are expecting their third child.
The Queen and members of both families are said to be delighted with the news. Prime Minister Theresa May greeted the news on Twitter as "fantastic."
The couple are already parents to Prince George, who celebrated his fourth birthday in July, and Princess Charlotte, who turned two in May.
Their third child would be fifth in line to the British throne. William, 35, is the eldest son of Prince Charles, the first in line to the throne, and a grandson of the queen. The announcement means Prince Harry is now sixth in line to the throne.
As with her previous two pregnancies, the Duchess is suffering from a rare form of acute morning sickness called Hyperemesis Gravidarum. She will no longer carry out her planned engagement at the Hornsey Road Children's Centre in London on Monday.
The severity of the condition, which affects 3.5 per 1,000 pregnant women, can cause dehydration, weight loss and a build-up of toxins in the blood or urine called ketosis. The 35-year-old is being cared for at Kensington Palace.
William and Kate were married at Westminster Abbey in 2011 after announcing their engagement in November 2010. The pair met at St Andrews University.