His Royal Highness The Duke of Edinburgh has died, Buckingham Palace has announced

The Queen and the Royal Family are in mourning following the death of Prince Philip, aged 99.

The Duke of Edinburgh, famously described by the Queen as her "constant strength and guide", passed away at Windsor Castle on Friday, Buckingham Palace announced shortly after midday.

He was the longest-serving consort in British history and dedicated decades of his life to royal duty, serving the nation at the monarch’s side.

Watch: The remarkable life of the longest-serving royal consort in British history

Despite coronavirus regulations, hundreds of mourners have laid flowers and paid their respects outside Buckingham Palace. Flags have been lowered to half mast across the country.

Buckingham 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 be made in due course.

“The Royal Family join with people around the world in mourning his loss.”

Hundreds of mourners laid flowers outside Buckingham Palace on Friday. Credit: PA

No further details were released about the circumstances of his death.

It is understood Prince Charles travelled to visit the Queen on Friday afternoon, travelling from his home in Gloucestershire to be by his mother's side at Windsor Castle.

Prince Harry and Meghan paid tribute to Philip on the website of their foundation Archewell, replacing its homepage with a memorial site and the words: “In loving memory of His Royal Highness The Duke of Edinburgh 1921-2021.

“Thank you for your service…You will be greatly missed.”

ITV News Royal Editor Chris Ship revealed Prince Harry is expected to travel from his home in America back to the UK to attend his grandfather's funeral.

As is tradition, Buckingham Palace placed a statement on its gate formally announcing the death of Prince Philip on Friday. Credit: PA

In a tribute recorded for ITV News before Philip’s death, the Princess Royal said about her father’s legacy: “Without him life will be completely different.

“But from society’s perspective he was able to keep pace with the kind of technological changes that have such an impact… but above all that it’s not about the technology it’s about the people.”

Philip had returned to Windsor Castle on March 16 to be reunited with the Queen after spending a month in hospital – his longest ever stay.

He initially received care for an infection but then underwent heart surgery for a pre-existing condition.

The Duke of Edinburgh and Queen Elizabeth II with their children in the garden of the Frogmore Estate, Berkshire. Credit: PA archive

Philip – father to the Prince of Wales, the Princess Royal, the Duke of York and the Earl of Wessex – was just two months away from his 100th birthday in June.

He spent much of the Covid-19 crisis staying with the Queen at Windsor in HMS Bubble – the nickname given to the couple’s reduced household of devoted staff during lockdown.

Prime Minister Boris Johnson pays tribute

Prime Minister Boris Johnson paid tribute to the Duke of Edinburgh in Downing Street and said “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”.

"Prince Philip earned the affection of generations here in the United Kingdom, across the Commonwealth and around the world," Mr Johnson said.

The Queen and the Duke of Edinburgh making their way down The Mall in an open topped Range Rover, in honour of the Queen's 90th birthday. Credit: PA

The Prime Minister paid tribute to "one of the last surviving people in this country to have served in the Second World War at Cape Matapan", remembering the Duke as an "expert carriage driver" and " a champion of the natural world".

Mr Johnson also paid tribute to the Duke of Edinburgh awards scheme but added we remember the Duke " above all 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.

"And it is to Her Majesty, and her family, that our nation’s thoughts must turn today.

"Because they have lost not just a much-loved and highly respected public figure, but a devoted husband and a proud and loving father, grandfather and, in recent years, great-grandfather.

"Speaking on their golden wedding anniversary, Her Majesty said that our country owed her husband “a greater debt than he would ever claim or we shall ever know” and I am sure that estimate is correct."

Downing Street said Cabinet "shared recollections" of meeting Prince Philip and praised his work, adding they had received thousands of messages of condolence from all over the world.

Labour leader Sir Keir Starmer said: “The United Kingdom has lost an extraordinary public servant in Prince Philip.

“Prince Philip dedicated his life to our country – from a distinguished career in the Royal Navy during the Second World War to his decades of service as the Duke of Edinburgh.

“However, he will be remembered most of all for his extraordinary commitment and devotion to the Queen.

“For more than seven decades, he has been at her side. 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.

“My thoughts are with the Queen, the Royal Family and the British people as our nation comes together to mourn and remember the life of Prince Philip.”

A member of the public leaves flowers outside Buckingham Palace. Credit: PA

US president Joe Biden and First Lady Jill Biden said they and the American people were keeping the Queen and the rest of the royal family "in our hearts".

In a statement, Mr Biden said: “Over the course of his 99-year life, he saw our world change dramatically and repeatedly. From his service during World War II, to his 73 years alongside the Queen, and his entire life in the public eye — Prince Philip gladly dedicated himself to the people of the UK, the Commonwealth, and to his family.

“The impact of his decades of devoted public service is evident in the worthy causes he lifted up as patron, in the environmental efforts he championed, in the members of the armed forces that he supported, in the young people he inspired, and so much more. His legacy will live on not only through his family, but in all the charitable endeavours he shaped."

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But it's not just public figures paying tribute. Members of the public have been placing bouquets at the front gates of Buckingham Palace.

Bunches of daffodils were among dozens floral tributes placed by the palace gates, with many people opting to wear masks while paying their respects.

Mounted police reminded those gathered to adhere to social distancing guidelines and remain two metres apart from other groups.

Flowers left outside Windsor Castle. Credit: PA

Hundreds of people travelled to Windsor Castle to pay their respects to the Duke of Edinburgh, describing him as “a man of principle who never veered from duty”.

Well-wishers young and old lined the street outside Windsor Castle near the town centre, as crowds of mourners were chaperoned by police to lay flowers and share messages of support to the royal family.