Queen Elizabeth and Prince Philip, with Prince Edward and Sophie, Duchess of Wessex behind them, are pictured in Aberdeenshire on Tuesday. The next day, Prince Philip was admitted to hospital. (Getty Images)
Prince Philip's third stay in hospital in the last eight months is expected to last a few more days.
The 91-year-old Duke of Edinburgh was admitted on Wednesday for a bladder infection, the same affliction that put him in hospital for five days in June.
"The Duke of Edinburgh is responding well to treatment," Buckingham Palace said in a statement on Thursday. "It is unclear when he will be discharged, but he is likely to remain in hospital for a few more days."
The BBC reported that the prince was being treated with antibiotics intravenously.
Despite his age, the news was a little surprising considering how active he had been lately. He attended several events during the Olympics, including the opening ceremony and equestrian, where he watched his granddaughter Zara Phillips compete. Earlier this week, he had been to yachting events on the Isle of Wight and reports are he appeared in good health.
In December, he underwent surgery for a blocked coronary artery. A few months later, his grandson Prince Harry remarked how the episode seemed to give Philip a "new spurt of life."
Indeed, instead of slowing down, Philip has almost made it a crusade to be out and about. Though he has given up a few of his responsibilities in the last few years, he has kept up a pace that has earned him new fans.
Dr. Eileen Burns of the British Geriatrics Society told the BBC that bladder infections were common, so the prince's latest bouts with it "may just be bad luck".
She also noted that immune systems become "less vigorous" in older people, when there's a higher risk of problems within the urinary tract.
PHOTO GALLERY: The life and times of Prince PhilipMILK AND SUGAR PLEASE ... HOLD THE WAX
British Vice Ambassador Andrew Noble, above, poses with wax figures of Catherine, Duchess of Cambridge and Prince William during a tea-and-scones media reception at the British embassy in Berlin on Thursday. The wax copies of the royal couple have arrived from London for a 12-week exhibition at Madame Tussauds. The figures, on loan from its London location, cost $230,000 each to make. Madame Tussauds made four wax statues of the couple for their first anniversary in April, each one showing Kate in a different dress. There are exhibitions in New York, Amsterdam and Blackpool as well. The Berlin waxworks features Kate in an Alice Temperley dress, which she wore to the "War Horse" movie premiere in January. (Reuters)