Prince Philip "passed away peacefully" on Friday morning at Windsor Palace, the Royal Family said.
Tributes have poured in from across the world for Prince Philip, the Queen's husband, who has died aged 99.
They praised the Duke of Edinburgh for his military service, tireless work for young people and his unwavering devotion to the Queen.
He "passed away peacefully" at Windsor Castle, to the west of London, on Friday morning, the Royal Family said.
How did Europe react?
The Spanish royal couple, King Felipe and Queen Letizia, sent a telegram to "Dear Aunt Lilibet".
"We shall never forget the moments we shared with him and the legacy of service and dedication to the Crown and the United Kingdom by your side," they wrote, signing: "All our love and affection."
Swedish King Carl Gustaf wrote in a statement that "the Queen and I were deeply saddened" about the announcement.
"Prince Philip has been a great friend of our family for many years, a relation which we have deeply valued. His service to his country will remain an inspiration to all," he added.
King Willem-Alexander, Queen Maxima and Princess Beatrix of the Netherlands also paid homage to the Duke, writing on Instagram: "Throughout his long life, he committed himself with dedication to the British people and to his many duties and responsibilities."
"His lively personality never ceased to leave an unforgettable impression," they said.
King Philippe and Queen Mathilde of Belgium said they were "saddened" by the Duke's passing.
"We wish to express our deepest condolences to Her Majesty The Queen, the British Royal Family and the people of the United Kingdom," they wrote.
The Danish Royal family said they sent their "personal condolences" to Queen Elizabeth, highlighting their personal connection to the Duke.
"Prince Philip was born in 1921 as Prince of Greece and Denmark and was a great-grandchild of Christian the 9th," they wrote.
The Norwegian Royal Family said it received the news of the Duke's passing "with great sorrow".
"His Majesty the King has decided that in connection with the death the flag will be flown at half-mast from the Palace balcony today and on the day of the funeral," the statement added.
Greek President Katerina Sakellaropoulou posted a picture of the Duke as a child, writing on Twitter that he "was born in Corfu" and that he had "served his country with devotion for many decades."
Both the Irish Taoiseach Micheal Martin and the European Commission President Ursula von der Leyen described themselves as "saddened" and extended their "thought and prayers" as well as their "sincere sympathy" to the Royal family and "the people of the United Kingdom."
Chancellor Angela Merkel saluted the Duke's "friendship with Germany, his straightforwardness and his sense of duty" which she said "will not be forgotten".
France's Emmanuel Macron sent his condolences to the Royal Family and British people for the loss of Prince Philip, who he said, had "lived an exemplary life defined by bravery, a sense of duty and commitment to the youth and the environment."
His Foreign Minister, Jean-Yves Le Drian, said the country "joins in the grief of its friends across the Channel" and paid tribute to "The European and British destiny of a man who was, not without panache, the contemporary of a century of trials and hopes for our continent".
The Kremlin said that President Vladimir Putin had sent a telegram to the Queen to express his "deep condolences".
"His Royal Highness's name is associated with many important events in your country's recent history. He rightly enjoyed the respect of the British and worldwide esteem," he said in the telegram.
Pope Francis also extended his "heartfelt condolences" in a telegram to the Queen.
"Recalling Prince Philip's devotion to his marriage and family, his distinguished record of public service and his commitment to the education and advancement of future generations, His Holiness commends him to the merciful love of Christ our Redeemer," the telegram said.
How did the rest of the world react?
US President Joe Biden and First Lady Jill Biden extended their condolences "on behalf of all the people of the United States".
"Over the course of his 99-year life, he saw our world change dramatically and repeatedly.
"The impact of his decades of devoted public service is evident in the worthy causes he lifted as patron," they continued. "His legacy will live on not only through his family, but in all the charitable endeavours he shaped."
Australian Prime Minister Scott Morrison said the Duke "embodied a generation that we will never see again".
"For nearly 80 years, Prince Philip served his Crown, his country and the Commonwealth," he added, highlighting that he had "presided as patron or president of nearly 50 organisations in Australia."
Indian Prime Minister Narendra Modi paid tribute to his "distinguished career in the military" and to the "many community service initiatives" he fronted. "May his soul rest in peace."
How did the UK react?
British Prime Minister Boris Johnson took to a pulpit outside Downing Street to pay his respects, saying that "Prince Philip earned the affection of generations here in the United Kingdom, across the Commonwealth and around the world."
He noted that the Duke had been "one of the last surviving people in this country to have served in the Second World War" and that "like the expert carriage driver that he was, 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."
He also praised him for being an environmentalist "long before it was fashionable" and for his "steadfast support for Her Majesty the Queen, not just as her consort, by her side every day of her reign, but as her husband, her strength and stay of more than 70 years."
The leader of the Anglican Church, the Archbishop of Canterbury, also emphasised the Duke's "powerful advocacy for conservation" in a statement.
"On the occasions when I met him, I was always struck by his obvious joy for life, his enquiring mind and his ability to communicate to people from every background and walk of life. He was a master at putting people at their ease and making them feel special," he also wrote.
Scotland's First minister Nicola Sturgeon said she was "saddened" by the news.
"I send my personal and deepest condolences — and those of the Scottish government and the people of Scotland — to Her Majesty The Queen and her family," she wrote on Twitter.
Keir Starmer, leader of the main opposition Labour Party, paid tribute to "an extraordinary public servant" who "dedicated his life to our country."
"However, he will be remembered most of all for his extraordinary commitment and devotion to the Queen.
"Their marriage has been a symbol of strength, stability and hope, even as the world around them changed — most recently during the pandemic. It was a partnership that inspired millions in Britain and beyond," he added.
Arlene Foster, First Minister of Northern Ireland, paid tribute to his "strong interest in Northern Ireland" and to his "profound and positive impact on thousands of our young people who found their purpose, passion and place in the world through participation in the Duke of Edinburgh's Awards."