Prince William is leaving his job as a search and rescue pilot for the Royal Air Force so he can concentrate on being a full time Royal.
Kensington Palace announced the news, saying it will give the Prince more time to focus on his charity work.
The Duke of Cambridge and his wife the Duchess will support the Queen by carrying out more official visits and appearances, both in the UK and abroad.
He has been a member of the Armed Forces for more than seven years.
He has previously spoken of his love for the job, saying: "There's no greater feeling than when you've actually done some good and saved someone's life."
When working for the RAF Prince William is known as Flight Lieutenant Wales.
He has rescued many people during his time working as a pilot, based in Anglesey, Wales.
The Duke and Duchess of Cambridge and Prince George are expected to move to a newly refurbished apartment in Kensington Palace within the coming weeks.