Prince Philip, Queen Elizabeth II's husband, has died aged 99, Buckingham Palace has announced.
A statement issued by the palace just after midday spoke of the Queen's "deep sorrow" following his death at Windsor Castle on Friday morning.
The Duke of Edinburgh, who was the longest-serving consort in British history, had returned to Windsor on 16 March after a month in hospital.
Boris Johnson said he "inspired the lives of countless young people".
There were tributes placed outside Windsor Castle by members of the public
"It is with deep sorrow that Her Majesty The Queen announces the death of her beloved husband," the palace said.
"The Royal Family join with people around the world in mourning his loss."
Speaking at Downing Street, the prime minister said that the duke had "earned the affection of generations here in the United Kingdom, across the Commonwealth, and around the world".
Tributes are paid from around the world to the Queen's "beloved" husband of 73 years, the longest-serving consort in British history.