Wellwishers gathered in the summer sun to help mark the Duke of Edinburgh's 96th birthday.
A message on Buckingham Palace's Twitter site read: "Wishing The Duke of Edinburgh a very happy 96th birthday today! #HappyBirthdayHRH".
The Duke, who is looking forward to his long-awaited retirement, was spending his special Saturday privately at Windsor Castle as a 41-gun royal salute boomed through Green Park in central London in his honour.
The King's Troop Royal Horse Artillery rode their horses and gun carriages across the Parade Ground to stage the gun salute.
Royal aides say the Duke is keen to enjoy more of his leisure time when he steps away from the limelight in a few months.
Next weekend, Philip is expected to help the Queen celebrate her official 91st birthday at the annual Trooping The Colour parade.
After his retirement, he may still appear occasionally at certain public events, but "will no longer play an active role by attending engagements", the Palace said.
The Duke joked about his advancing age and retirement when he attended his final Buckingham Palace presentation ceremony for his Duke of Edinburgh Award scheme in May.
He told TV chef Prue Leith: "I'm discovering what it's like to be on your last legs."
Philip of Greece and Denmark was born on the island of Corfu on June 10 1921 to Prince Andrew of Greece and Princess Alice of Battenberg.
His early years were marked by upheaval after the family went into exile following a military coup in Greece which overthrew Philip's uncle, King Constantine I.
He moved to England to stay with relatives and study at Cheam Prep School in 1928, before spending a year at Salem School in south Germany, then finally enrolling at Gordonstoun School in Morayshire.
Philip went on to join the Royal Navy and, while a cadet, he caught the eye of a 13-year-old Princess Elizabeth.
He served with distinction during the Second World War and his friendship with the Princess grew into love.
They married two years after the end of the war.
Within five years, George VI had died and Princess Elizabeth had become Queen.
The Duke, who is known for his no-nonsense approach and acerbic wit, is the longest serving consort in British history and also the oldest serving partner of a reigning monarch.