PHOTOS: The life of Prince Philip

LONDON (Nexstar) — Prince Philip, the Duke of Edinburgh died Friday at the age of 99, Queen Elizabeth announced.

“His Royal Highness passed away peacefully this morning at Windsor Castle,” the Royal Family wrote in a statement. “Further announcements will (be) made in due course. The Royal Family join with people around the world in mourning his loss.”

Philip spent a month in hospital earlier this year before being released on March 16 to return to Windsor Castle.

He had been transferred on March 1 to a specialized London heart hospital to undergo testing and observation for a pre-existing heart condition as he continued treatment for an unspecified infection. Philip had previously been admitted to the private King Edward VII Hospital hospital in February for several days after feeling unwell.

LONDON, ENGLAND – JUNE 12: (L-R) Queen Elizabeth II and Prince Philip, Duke of Edinburgh during “The Patron’s Lunch” celebrations for The Queen’s 90th birthday at The Mall on June 12, 2016 in London, England. (Photo by Jeff Spicer/Getty Images)
Britain’s Queen Elizabeth II (L) and Britain’s Prince Philip, Duke of Edinburgh (R) chat while seated during a musical performance in the Abbey Gardens, Bury St Edmunds, during her Golden Jubilee visit to Suffolk, east of England, on July 17, 2002. (Photo by Fiona HANSON / POOL / AFP) (Photo by FIONA HANSON/POOL/AFP via Getty Images)
KING’S LYNN, ENGLAND – DECEMBER 25: Princess Beatrice, Princess Eugenie, Princess Anne, Princess Royal, Prince Andrew, Duke of York, Prince William, Duke of Cambridge, Prince Philip, Duke of Edinburgh, Catherine, Duchess of Cambridge, Meghan Markle and Prince Harry attend Christmas Day Church service at Church of St Mary Magdalene on December 25, 2017 in King’s Lynn, England. (Photo by Chris Jackson/Getty Images)
Former South African president Nelson Mandela (L) chats with the Duke of Edinburgh, Prince Philip at Drakenstein Prison, Paarl about 50 kms outside of Cape Town 05 November 2000. The two men attended an awards ceremony for juvenile prisoners held under the auspices of the International Awards Association, a development programme for young people. (Photo by ANNA ZIEMINSKI / AFP) (Photo by ANNA ZIEMINSKI/AFP via Getty Images)
(L to R) The Duke of Edinburgh, Prince William, Earl Spencer, Prince Harry and Prince Charles walk outside Westminster Abbey during the funeral service for Diana, Princess of Wales, 06 September. Hundreds of thousands of mourners lined the streets of Central London to watch the funeral procession. The Princess died last week in a car crash in Paris. (Photo credit should read JEFF J. MITCHELL/AFP via Getty Images)
Britain’s Queen Elizabeth II (L) delivers a speech 06 December 2000 during the state opening of Parliament in the House of Lords in London as her husband, the Duke of Edinburgh (R), listens. AFP PHOTO POOL DAILY MAIL/MIKE FORSTER (Photo credit should read MIKE FORSTER/AFP via Getty Images)
Britain’s Queen Elizabeth II (L), her husband Prince Philip, Duke of Edinburgh (R) and members of the Royal Family wave to the crowd on June 3, 1972 from the balcony of Buckingham Palace in London, during the Trooping the Colour ceremony. (Photo by – / AFP) (Photo by -/AFP via Getty Images)
HM Queen Elizabeth II and Prince Philip, the Duke of Edinburgh, wearing formal dress as they attend a concert at Festival Hall, London, May 1951. (Photo by Hulton Archive/Getty Images)
Undated portrait of Prince Philip of Greece, later Philip Mountbatten, Duke of Edinburgh. (Photo by – / AFP) (Photo by -/AFP via Getty Images)
Britain’s Princess Elizabeth (future Queen Elizabeth II) and her husband Philip, Duke of Edinburgh, pose during their honeymoon, November 25, 1947 in Broadlands estate, Hampshire. (Photo by – / – / AFP) (Photo by -/-/AFP via Getty Images)
Undated picture showing the Royal British couple, Queen Elizabeth II, and her husband Philip, Duke of Edinburgh, with their two children, Charles, Prince of Wales (L) and Princess Anne (R), circa 1951. (Photo credit should read OFF/AFP via Getty Images)
LONDON, ENGLAND – JUNE 12: (L-R) Queen Elizabeth II and Prince Philip, Duke of Edinburgh during “The Patron’s Lunch” celebrations for The Queen’s 90th birthday at The Mall on June 12, 2016 in London, England. (Photo by Jeff Spicer/Getty Images)
The Duke of Edinburgh opens the Gorilla Kingdom at London Zoo, 29 March 2007. The new habitat has ditched conventional cages and bars for the environs of an African rainforest and is already being dubbed the “Love Island”. AFP PHOTO POOL/Steve Parsons/WPA Rota (Photo by STEVE PARSONS / POOL / AFP) (Photo by STEVE PARSONS/POOL/AFP via Getty Images)
LONDON, ENGLAND – AUGUST 2: Prince Philip, Duke of Edinburgh, (C) in his role as Captain General, Royal Marines, makes his final individual public engagement as he attends a parade to mark the finale of the 1664 Global Challenge, on the Buckingham Palace Forecourt on August 2, 2017 in London, England. (Photo by Hannah McKay – WPA Pool/Getty Images)
Britain’s Queen Elizabeth II and Britain’s Prince Philip, Duke of Edinburgh (R) during the wedding ceremony of Britain’s Prince Harry, Duke of Sussex and US actress Meghan Markle in St George’s Chapel, Windsor Castle, in Windsor, on May 19, 2018. (Photo by Jonathan Brady / POOL / AFP) (Photo by JONATHAN BRADY/POOL/AFP via Getty Images)
EDINBURGH, UNITED KINGDOM – JULY 04: Prince Philip, Duke of Edinburgh smiles during a visit to the headquarters of the Royal Auxiliary Air Force’s (RAuxAF) 603 Squadron on July 4, 2015 in Edinburgh, Scotland. (Photo by Danny Lawson – WPA Pool/Getty Images)
KING’S LYNN, ENGLAND – DECEMBER 25: (L-R) Prince William, Duke of Cambridge, Prince Philip, Duke of Edinburgh, Catherine, Duchess of Cambridge, Meghan Markle and Prince Harry attend Christmas Day Church service at Church of St Mary Magdalene on December 25, 2017 in King’s Lynn, England. (Photo by Chris Jackson/Getty Images)
SOUTH QUEENSFERRY, SCOTLAND – SEPTEMBER 04: Queen Elizabeth II, Prince Philip, Duke of Edinburgh and First Minister Nicola Sturgeon attend the official opening ceremony of the Queensferry Crossing, on September 4, 2017 in South Queensferry, Scotland. Scotland’s newest road bridge which began construction in 2011, crosses the Firth of Forth near Edinburgh. The crossing is the world’s longest three tower cable stayed bridge. (Photo by Andrew Milligan – WPA Pool/Getty Images)
LONDON, ENGLAND – MARCH 16: Prince Philip, Duke of Edinburgh is seen leaving King Edward VII Hospital on March 16, 2021 in London, England. The Duke of Edinburgh has today been discharged from King Edward VII’s Hospital and has returned to Windsor Castle, following treatment for an infection and a successful procedure for a pre-existing condition. (Photo by Jeff Spicer/Getty Images)
WINDSOR, ENGLAND – JULY 22: Prince Philip (R), Duke of Edinburgh arrives for the transfer of the Colonel-in-Chief of The Rifles ceremony at Windsor castle on July 22, 2020 in Windsor, England. The Duke of Edinburgh has been Colonel-in-Chief of The Rifles since its formation in 2007. HRH served as Colonel-in-Chief of successive Regiments which now make up The Rifles since 1953. The Duchess of Cornwall was appointed Royal Colonel of 4th Battalion The Rifles in 2007. (Photo by Adrian Dennis – WPA Pool/Getty Images)
WINDSOR, ENGLAND – MAY 18: Prince Philip, Duke of Edinburgh talks to Prince Harry, Duke of Sussex and Lady Helen Taylor as they leave after the wedding of Lady Gabriella Windsor to Thomas Kingston at St George’s Chapel, Windsor Castle on May 18, 2019 in Windsor, England. (Photo by Steve Parsons – WPA Pool/Getty Images)
TOPSHOT – Britain’s Queen Elizabeth II (L) and Britain’s Prince Philip, Duke of Edinburgh (R) wait for the carriage carrying Princess Eugenie of York and her husband Jack Brooksbank to pass at the start of the procession after their wedding ceremony at St George’s Chapel, Windsor Castle, in Windsor, on October 12, 2018. (Photo by Alastair Grant / POOL / AFP) (Photo by ALASTAIR GRANT/POOL/AFP via Getty Images)
WINDSOR, ENGLAND – OCTOBER 12: Prince Philip, Duke of Edinburgh attends the wedding of Princess Eugenie of York to Jack Brooksbank at St. George’s Chapel on October 12, 2018 in Windsor, England. (Photo by Alastair Grant – WPA Pool/Getty Images)

Philip’s illness was not believed to be related to COVID-19. Both he and the queen, 94, received a first dose of a coronavirus vaccine in early January.

The royal household had been planning celebrations to mark Philip’s 100th birthday on June 10, lockdown restrictions permitting.

Philip, also known as the Duke of Edinburgh, retired from public duties in 2017 and rarely appears in public. During England’s current coronavirus lockdown, he has been staying at Windsor Castle, west of London, with the queen.

Philip married the then-Princess Elizabeth in 1947 and is the longest-serving royal consort in British history. He and the queen have four children, eight grandchildren and nine great-grandchildren.

The youngest great-grandchild, son of Princess Eugenie and her husband Jack Brooksbank, was born Feb. 9 and was named Augustus Philip Hawke Brooksbank, with one of his middle names a tribute to the Duke of Edinburgh.

The Associated Press contributed to this report.