Prince William and Duchess Catherine are expecting their third child.

The royal couple - who are already parents to Prince George, four, and two-year-old Princess Charlotte - are set to expand their family further next year, Kensington Palace have announced.

A statement from Kensington Palace read: "Their Royal Highnesses the Duke and Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting their third child.

"The Queen and both their families are delighted with the news."

Catherine is once again suffering from Hyperemisis Gravidarum - a debilitating form of serious morning sickness - and has cancelled a planned official engagement in London on Monday (04.09.17).

The statement concluded: "As with her previous two pregnancies, the Duchess is suffering from Hyperemisis Gravidarum. Her Royal Highness will no longer carry out her planned engagement at the Hornsey Road Children's Centre in London today. The Duchess is being cared for at Kensington Palace."

The happy news comes in the same week that the couple - who recently relocated to Kensington Palace, London - were due to commence full-time royal duties once their son George starts at Thomas's School in Battersea, south west London, on Thursday (07.09.17).

A series of tweets on the official Kensington Palace Twitter account last week read: "The coming months will see The Duke & Duchess & Prince Harry undertake a busy autumn programme as TRH return to royal duties & engagements.

"Over the course of the autumn, TRH will visit a number of communities, charities and organisations across the UK.

"TRH will continue to highlight the important work of their patronages, & collectively focus on supporting issues surrounding mental health. (sic)"