After retiring from public duties following a lifetime of service, a spokeswoman confirmed the Queen’s husband is marking the occasion in private.
The Duke of Edinburgh did not attend his wife’s official birthday celebrations on Saturday, when other senior royals gathered to watch the Trooping the Colour parade.
Born in 1921 on the Greek island of Corfu, Prince Philip has kept a low profile since his final public engagement in August – the last of 22,219 attended since the Queen ascended to the throne in 1952.
He did, however, attend the wedding of his grandson Prince Harry and Meghan Markle at Windsor Castle on 19 May – a few weeks after undergoing a hip replacement operation.
The former naval officer, famous for his no-nonsense style, has rarely celebrated his birthday. During his working years, he often used to attend engagements as normal.
The prince arrived with the Queen by car to the wedding of Harry and Meghan, now the Duke and Duchess of Sussex, waving to the crowds at Windsor Castle.
Dressed in a morning suit, he got out of the car with no apparent trouble, despite the hip surgery.
He walked steadily with his hands clasped behind his back, exchanging pleasantries with Harry and William before taking his seat in St George’s Chapel.
During firebrand US pastor Michael Curry’s near 14-minute sermon on the power of love, he sat stony faced as other royals looked visibly bemused at the preacher’s theatrical style and off-script performance.
Prince Philip was a patron, president or member of more than 780 organisations and he went on 637 visits abroad on his own, giving almost 5,500 speeches.
He has spent much of his time at Windsor since retiring and also stays at the Queen’s private Sandringham estate in Norfolk.
Although the Duke has officially retired, his roles within the Royal Family continue.
While the Queen concentrates on affairs of state, Prince Philip is in charge of running the royal estates and maintains a small office dealing with correspondence.
In recent years, the Duke has made the headlines with his politically incorrect ice breakers when meeting the public.
The hugely popular television series The Crown, which began airing in 2016, brought the prince’s life and role in the Royal Family under the spotlight as it traced the Queen’s life from their wedding in 1947.
The series brought into focus the role the prince played in supporting the young Queen after she came to the throne following the early death of her father King George VI in 1952, when she was just 25.
Actor Matt Smith, who played the early Philip in The Crown, described him as a “roguish, brilliant man”.
He told The Observer: “I just think he’s a bit of a cool cat.
“And that’s what I love about him. He’s done what he wants, when he wants, how he wants, with whom he wants. And his wife’s the Queen.”