Never one for a fuss -- least of all over himself -- Queen Elizabeth II's husband has no plans for celebrations as he moves a step nearer to 100.
"He will be spending it privately," a Buckingham Palace spokeswoman told AFP, without saying where.
The Duke of Edinburgh was absent as planned from his wife's official birthday celebrations on Saturday, when other senior royals gathered to watch the Trooping of the Colour military parade in London.
He has kept a low profile since conducting his final solo public engagement in August, the last of 22,219 attended since the queen ascended to the throne in 1952.
However, he did attend the wedding of his grandson Prince Harry and Meghan Markle at Windsor Castle on May 19, despite undergoing a hip replacement on April 4.
The no-nonsense former naval officer has rarely celebrated his birthday and, in his working years, often used to turn out for engagements as normal.
- Back on his feet -
At the wedding of Harry and Meghan, now the Duke and Duchess of Sussex, the prince arrived by car with the queen, waving to the crowds at Windsor Castle.
Wearing a morning suit, he got out of the car with no apparent trouble, despite recent hip surgery.
He walked hands clasped behind his back, exchanging pleasantries with Harry and his brother Prince William as he took his seat in St. George's Chapel.
He was pictured keeping a poker face during firebrand US pastor Michael Curry's near-14 minute sermon on the power of love -- no mean feat as other royals looked visibly bemused at the preacher's theatrical style and off-script free-styling.
Prince Philip was the patron, president or member of more than 780 organisations. He carried out 637 visits abroad on his own and gave almost 5,500 speeches.
Since retiring, he has spent much of his time at Windsor, west of London, and at the queen's private Sandringham estate in Norfolk, eastern England, with occasional visits to London.
He has also been spotted carriage driving -- a sport he took up in the 1970s after stopping playing polo.
Although the duke has stepped down from public duties, his roles within the royal family continue.
While Queen Elizabeth concentrates on affairs of state, Prince Philip is in charge of matters such as running the royal estates.
He maintains a small office dealing with correspondence.
- Role reappraisal -
In recent years, the duke has been caricatured as a gruff old stick-in-the-mud, making headlines with his politically incorrect ice-breakers when meeting the public.
But his role has been re-appraised since the blockbuster television series "The Crown" started airing in 2016, tracing the queen's life from their wedding in 1947.
The series shows the role that Prince Philip played in supporting the young queen after she was thrust onto the throne by the early death of her father king George VI in 1952, when she was 25.
His shrewdness, steadfastness and impatience for change are reflected in the series, forcing a reassessment of the royal stalwart.
Actor Matt Smith, who played the early Philip in "The Crown", described him as a "roguish, brilliant man".
"I just think he's a bit of a cool cat," he told The Observer newspaper.
"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."