Prince Philip, the lifelong companion of Britain's Queen Elizabeth II, has died, Buckingham Palace announced Friday. He was 99.

In a statement, the palace said: “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.

The duke had been admitted to the King Edward VII Hospital in London hospital on February 17 after feeling unwell. The palace later confirmed that he was being treated for an infection. On March 1, he was transferred to St. Bartholomew's Hospital, also in London, where doctors continued to treat the infection as well as undertake testing for a pre-existing heart condition. After heart surgery, the duke was discharged from hospital in mid-March.

Philip, also known by his official title of the Duke of Edinburgh, was the longest-serving British consort. He married the then Princess Elizabeth in 1947 after a courtship that charmed a country still reeling from the ravages of World War II.

In his seven decades of service, Philip often accompanied the Queen on royal engagements, and conducted thousands of his own solo appearances. He once referred to himself as “the world's most experienced plaque unveiler,” while the Queen lauded him as her “constant strength and guide.”

The duke was known for off-the-cuff remarks that often displayed a quick wit but occasionally missed the mark, sometimes in spectacular fashion. Philip continued making public appearances well into his 90s, retiring only in August 2017.

He supported a number of philanthropic endeavors and was associated with around 800 organizations. He founded the Duke of Edinburgh Awards Scheme, a youth development program that operates in more than 130 countries and territories around the world.

After retiring, Philip spent much of his time at the Queen's rural Sandringham estate. He was occasionally seen in later years at private family events such as the weddings of the Duke and Duchess of Sussex, and of Princess Eugenie to Jack Brooksbank, both at Windsor Castle.

Philip's advanced age meant that his health had been the subject of much media focus in recent years. In December 2019, he was taken to hospital as a “precautionary measure” for what Buckingham Palace described as a “pre-existing” condition. He had previously been admitted to hospital on multiple occasions for a variety of reasons, including for a hip replacement and for treatment for bladder infections.

The duke was born the Prince Philip of Greece and Denmark on the Greek island of Corfu in 1921. He left Greece aged 18 months with his family when King Constantine was forced to abdicate after a revolt by Greece's war-stretched military forces. The family moved first to Paris and later, in 1928, to England.

Philip had an itinerant childhood, educated variously in the UK, France, and Germany.

He became a decorated naval officer for his service during World War II, and when peace returned, rekindled an earlier friendship with Elizabeth that quickly blossomed into a public romance.

In order to marry, the duke renounced his Greek title, became a naturalized British subject and took the surname Mountbatten, derived from his mother's side of the family. The marriage ceremony was held at Westminster Abbey in 1947. He and Elizabeth had four children: Charles, Anne, Andrew and Edward.

CNN's Laura Smith-Spark contributed to this report.