Prince Philip, the Duke of Edinburgh, who served as consort to his wife Queen Elizabeth II for more than 60 years, has died at the age of 99.
Buckingham Palace released a statement at 12:00pm local time (9:00pm AEST), confirming the duke had died "peacefully" on Friday morning.
"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 statement read.
"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."
British Prime Minister Boris Johnson said the country mourned with the Queen and offered condolences to her and her family.
"We remember the duke for all of this and above all for his steadfast support for Her Majesty the Queen," Mr Johnson said.
"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."
Flags at Buckingham Palace and on government buildings across the country have been lowered to half-mast.
Speaking at Downing Street, Mr Johnson said the duke had earned the "affection of generations here in the United Kingdom, across the Commonwealth, and around the world".
"He was the longest-serving consort in history, one of the last surviving people in this country to have served in the Second World War at Cape Matapan, where he was mentioned in dispatches for bravery and in the invasion of Sicily, where he saved his ship by his quick thinking and from that conflict he took an ethic of service that he applied throughout the unprecedented changes of the post-war era.
"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."
Australian Prime Minister Scott Morrison said Prince Philip "embodied a generation that we will never see again", and paid tribute to his service to Australia and the Commonwealth.
"Australians send our love and deepest condolences to her Majesty and all the Royal family," he said in a statement.
"The Commonwealth family joins together in sorrow and thanksgiving for the loss and life of Prince Philip.
"God bless from all here in Australia."
Mr Morrison confirmed flags around the country will be lowered "in honour of His Royal Highness".
As per Prince Phillip's wishes for a "no-fuss" farewell, the College of Arms has confirmed his funeral will not be a State Funeral and he will not lie in state.
The duke's body will lie at rest in Windsor Castle and the funeral will take place in St George's Palace in the castle's grounds, at a time yet to be determined.
Due to England's current COVID-19 restrictions, funerals are limited to a maximum of 30 attendees, although it is not known if this will be the case for the duke's funeral.
From Greek royalty to Britain's longest-serving consort
Born on the Greek island of Corfu in 1921, Philip was the fifth child and only son of Prince Andrew of Greece and Denmark and Princess Alice Battenberg — a great-granddaughter of Queen Victoria.
His family had to flee Greece after his uncle, King Constantine, was forced to abdicate in 1922. Philip and his mother spent several years exiled in France before he ended up in boarding school in England.
Philip joined the Royal Navy as a cadet in 1939 and one of his first duties was to entertain a young Princess Elizabeth and her sister Margaret during a royal tour of a naval college in Dartmouth.
Philip, who was 18, left a lasting impression on the 13-year-old future monarch and the pair began exchanging letters, which blossomed into a romance as Philip began spending Christmases with the royal family at Windsor Castle during the war.
The pair married in 1947 and Philip went on to become the longest-serving consort of a monarch in the history of the British royal family.
The duke had a long career with the Royal Navy, serving on the HMS Valiant during the Second World War where he was commended for his actions during the Battle of Cape Matapan, in Greece during 1941.
He was later promoted to first lieutenant and was aboard the HMS Wallace in Tokyo Bay when the Japanese surrendered in September 1945.
In 1950, at age 28, he took command of the HMS Magpie but his navy career was ultimately curtailed by the death of King George VI, Elizabeth's father, in 1952.
Duke's recent health issues
The duke had suffered failing health in recent years and retired from royal duties in 2017.
On March 16 he had been released from London's King Edward VII hospital, after being admitted a month before as a "precautionary measure".
A statement from Buckingham Palace at the time of his admission said he had been sent to hospital on the advice of his doctor after feeling unwell.
A week later the Palace said he was battling an "infection" and would be staying in hospital.
However, the royal family continued to give an upbeat assessment of his health, with his youngest son Prince Edward saying he was "a lot better" and was "looking forward to getting out".
On March 1, Prince Philip was transferred to St Bartholomew's hospital, also in London, where tests were carried out on a pre-existing heart condition. A procedure for that condition was successfully carried out on March 4.
"His Royal Highness will remain in hospital for treatment, rest and recuperation for a number of days," the palace said afterwards. He was later sent back to Edward VII to recover.
Prince Philip was previously admitted to King Edward VII just before Christmas in 2019 for treatment for a pre-existing condition, and remained there for several days.
The prince, who would have turned 100 in June, retired from public life in August 2017 but occasionally made appearances at royal engagements.
He spent Christmas 2011 in hospital after an operation to clear a blocked artery and he missed the end of celebrations to mark the Queen's 60th year on the throne in 2012 after being hospitalised with a bladder infection.
In 2013, he underwent "an exploratory operation following abdominal investigations".
He was admitted to hospital in 2017 for treatment for an infection, also arising from a pre-existing condition, and last year spent 10 days in hospital for hip replacement surgery.
In January 2019, Prince Philip was unhurt when his Land Rover flipped after a collision with another car near Sandringham.
He gave up his driving licence after police gave him a warning for driving without wearing a seatbelt.
Known for his forthright manner, Prince Philip was a key source of support for the Queen, who described him as her "strength and stay" throughout their 73-year marriage and her record-breaking reign.
Prince Philip is survived by his wife the Queen and his children Prince Charles, Princess Anne, Prince Andrew and Prince Edward and their families.