Prince Philip has died aged 99, Buckingham Palace has announced.
The Duke of Edinburgh was the longest-serving consort in British history.
The duke and the Queen were married for more than 70 years and Philip dedicated decades of his life to royal duty, serving the nation at the monarch's side.
He officially retired from public engagements in the summer of 2017.
The Palace said in a statement: "It is with deep sorrow that Her Majesty The Queen announces the death of her beloved husband, His Royal Highness The Prince Philip, Duke of Edinburgh.
"His Royal Highness passed away peacefully this morning at Windsor Castle.
"Further announcements will made in due course.
"The Royal Family join with people around the world in mourning his loss."
Life and work of the Duke of Edinburgh
Prince Philip was born in Corfu, Greece, on 10 June 1921. He was the only son of Prince Andrew of Greece and his mother was Princess Alice of Battenberg, hence giving him the title of 'Prince of Greece and Denmark'.
Prince Philip and his family had to leave Greece when he was just 18 months old, due to the political instability of the country. His uncle, Constantine I, the King of Greece, was forced to abdicate.
During the First World War, Prince Philip's grandfather, Prince Louis of Battenberg, changed the family's name to Mountbatten.
Prince Phillip adopted this name when he became a naturalised British subject and renounced his Royal title in order to marry the then Princess Elizabeth. He was then bestowed with the titles Duke of Edinburgh, Earl of Merioneth and Baron Greenwich.
The duke had a successful naval career, during which he saw active service in the Second World War.
His Royal Highness then focused on his work supporting the Queen after she ascended the throne in 1952.
The duke became the longest serving British consort - in companion to the Sovereign - in 2009 and founded the Duke of Edinburgh's Award in 1956.
The palace announced in May 2017 that the duke had decided, with full support of the Queen, to officially retire from public duties.