The new baby will be eighth in line to the throne.
The first seven places will remain unchanged – the Prince of Wales, the Duke of Cambridge, Prince George, Princess Charlotte, Prince Louis, Harry, and Archie Mountbatten-Windsor.
The Duke retained his place in the line of succession despite quitting royal life, and dropping his HRH style.
When the new addition arrives, the Duke of York, who was born second in line in 1960, will move down to ninth place.
Last November, the Duchess of Sussex wrote a deeply personal account of suffering a miscarriage after she decided to speak out in order to encourage others to do the same, to encourage others to listen and in doing so, lighten the load for others who are grieving.
In an opinion piece titled The Losses We Share for the New York Times, the Duchess revealed that she had lost her unborn, second child in July.
She described the experience as “an almost unbearable grief experienced by many but talked about by few”.
This is a breaking news story and we will update it when we know more.