The Duke of Edinburgh was Prince Philip's official name. He had been by his wife's side as she led the country for 69 years. She has been queen longer than any other ruler in British history.
The British royal family 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 be made in due course. The Royal Family join with people around the world in mourning his loss."
Philip was born into the royal families of Greece and Denmark. His father was Prince Andrew of Greece and Denmark and his mother was Princess Alice of Battenberg. Philip married Elizabeth in 1947.
He helped to bring the British royal family tradition into modern life after World War Two. In Buckingham Palace, the official royal family home, he was said to be the one person the queen could turn to and trust.
'My strength and stay'
"He has, quite simply, been my strength and stay all these years," Elizabeth said in a speech marking the 50th anniversary of their marriage in 1997. "I, and his whole family, and this and many other countries, owe him a debt greater than he would ever claim, or we shall ever know."
Philip spent four weeks in the hospital earlier this year. He received treatment for an infection and had surgery on his heart. He died just two months before he was to celebrate his 100th birthday.
Buckingham Palace and government buildings across Britain lowered their flags. There are no public details about his funeral yet. But the ceremonies are likely be smaller and quieter than usual for royal deaths. That would reflect Philip's well-known dislike of a big production.
At times, Philip was known for comments considered as sexist and racist. The prince also completed more than 20,000 appearances as senior member of the royal family to help British interests at home and around the world. He headed organizations that help others in need and helped raise his four children, including Prince Charles, the heir to the throne. Philip retired from public life in August 2017.
Gave up a military career
A former naval officer, Philip admitted he found it hard to give up his military career to take on the job as the queen's partner. The prince once said to his old friend that his job "first, second and last — was never to let her [the queen] down."
British Prime Minister Boris Johnson said of Philip, "he helped to steer the royal family and the monarchy so that it "remains an institution indisputably vital to the balance and happiness of our national life."
The British opposition leader Keir Starmer added, "He will be remembered most of all for his extraordinary commitment and devotion to The Queen."
I'm Jonathan Evans.