The Duke of Edinburgh, Prince Philip has died

The Duke of Edinburgh, as he was officially known, had been by his wife's side throughout her 69-year reign, the longest in British history, during which time he earned a reputation for a tough, no-nonsense attitude and a propensity for occasional gaffes.

"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," the palace said in a statement.

"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."

A Greek prince, he married Elizabeth in 1947 playing a key role in modernising the monarchy in the post-World War Two period, and behind the walls of Buckingham Palace being the one key figure the queen could turn to and trust.

"He has, quite simply, been my strength and stay all these years," Elizabeth said in a rare personal tribute to Philip made in a speech marking their 50th wedding anniversary in 1997.