The Duke of Edinburgh may have been more prone to developing his bladder infection because of conditions during Sunday's Diamond Jubilee Pageant, experts have said.
Philip showed his determination to spend the day by the Queen's side, standing next to her on the deck of the Royal Barge for much of the pageant, which resulted in the couple spending three hours in wet and cold conditions.
Harley Street doctor Malcolm Vandeburg said that stress, potentially brought on by the high-profile Jubilee celebrations could have led the infection to emerge when it did.
Prince Philip spent Sunday on the royal barge next to the Queen, despite the cold, wet conditions
A specialist in general medicine and male health problems, Dr Vandeburg also said the Duke may not have made enough visits to the toilet while on board the royal barge.
Dr Vandeburg said if Philip contracted the infection prior to the boating extravaganza, he might have been in considerable pain as he waved to crowds.
"To think he could have had that and stood up all day makes it all the more remarkable, on the assumption it didn't just start the moment they announced it," he said.
"Given his health and the care he will undoubtedly get, I wouldn't be unduly concerned."
He added: "If a man gets a bladder infection, it's usually that something else is going wrong as well.
"In a man of around 90, the thing that you would think of is some form of bladder outlet obstruction which would, at the top of the list, be some form of obstruction around the prostate.
"This would cause urine to remain in the bladder, causing an infection
Consultant urological surgeon Dr Frank Chinegwundoh agreed with Dr Vandeburg saying that bladder infections are caused by bugs already in the system, but the conditions on Sunday may have caused it to develop.
Not drinking enough and infrequent visits to the toilet while on the Spirit of Chartwell may have also contributed to him developing the infection, Dr Frank Chinegwundoh said.
Dr Chinegwundoh, from Barts Health NHS Trust in London, said the most likely cause of the infection was something to do with Philip's prostate gland, but conditions on Sunday would not have helped.
"I don't think it helps, because he would not have had a lot of fluids nor would he have been peeing to wash out any bugs and all the wet and cold might have reduced his immune system so I think the combination of everything may have led to this.
"Urine infections are generally caused by bugs that are in your own body naturally, so it would not have been that he picked it up from somewhere during the pageant.
"It's not that it would have caused it but, because of the circumstances he was in, it's possible that he would not have been able to get rid of it. It might have predisposed him to it."
He said bladder infections are often caused because of issues with the prostate gland, and when infections are not properly "flushed out", creating a "stagnant pond" effect.
Dr Chinegwundoh said the best treatment is rest, fluids and antibiotics and the Duke would probably have had an ultrasound as well.
"The first thing would be to make sure he is hydrated and give him antibiotics, probably intravenously at first, and if there's some prostate problems then that can be dealt with."
He said bladder infections are usually easily treated, adding: "If you treat it early with the appropriate antibiotics then it should clear up within days so I wouldn't have thought it a great cause of concern.
"If you left it long enough and didn't treat with antibiotics then the infection could spread from the urinary system into the blood and that is potentially fatal.
"But it seems like the signs were recognised and he was treated fairly swiftly."