The Duke of Edinburgh has been admitted to hospital in central London for planned surgery on his hip, Buckingham Palace has said.
The surgery will take place on Wednesday at the King Edward VII Hospital in Marylebone.
By James Gallagher, BBC health and science correspondent
Surgery at any stage of life carries risks.
But patients are not ruled out of surgery based on their age alone.
For patients like Prince Philip, overall fitness is a bigger factor than how old they are.
This will be a decision between patient and surgeon assessing the benefits and the risks of the planned procedure.
In general, frailty increases with age and does increase the risks of major surgery.
We do not know what type of hip operation Prince Philip is having.
Most hip replacement operations in the UK take place on patients between the ages of 60 and 80.
However, such operations do take place even later in life.
Peter Kay, professor of orthopedics at Manchester University and a council member of the Royal College of Surgeons, said the most common reason older patients were admitted for planned hip surgery was for a hip replacement, usually due to osteoarthritis or a fracture.
He said between one and two percent of hip replacements were performed on people in their 90s and that the mortality rate had halved in the last few years to just 0.25 per cent.
"It is a relatively safe procedure," he told The Telegraph.
"You have to make sure the patient is fit and well but generally speaking, you will be in hospital around five days and spend six to eight weeks using crutches before walking independently and carrying on with normal life."
I hope nothing bad happens!
Didn't the late Queen Mother also have a hip operation at the age of 95?
Actually, I just looked it up and the Queen Mum had a hip replacement surgery done in 1998 at the age of 97. It was successful.
Queen Visits Her Mother, 97, Who Had A Hip Replacement - tribunedigital-chicagotribune
The Queen Mother underwent a hip replacement on her right hip at the same hospital in 1995, at the age of 95, and another, on her left hip, aged 97, in 1998.
Hopefully he will be in good spirits for the wedding, even if he perhaps needs help (cane/wheel chair) for it. He wouldn't miss it.
Philip is too active and too stubborn of a man to let something like this keep him down. He's going to be rarin' to go and in good form in time for the wedding come hell or high water. He's got that kind of spunk and determination to make it so.
Depending on the person hip surgery recovery can go pretty quickly. They get you up and walking the day of surgery or day after. P.T. usually runs a couple months if needed...I can't imagine Phillip not being at the wedding. He's a tough old guy and in good physical condition. That can help his recovery time. LaRae
It's interesting to read how many people think Philip is going to be 'stubborn' about attending the wedding. Wishful thinking. At least I don't wish that kind of bull-headedness from him at this stage of life while recovering from major surgery at his age. Let the man be, I say. He's retired for a reason.
Having a seriously ailing relative at a wedding with the possibility of complications ensuing because of their attendance would not be anything I'd want on my conscience. The bride and groom can visit him, or he can be present at the reception in privacy. He doesn't need to be at the church in front of cameras to prove anything. JMO.
No doubt. If he was still in hospital, if he had to commandeer an ambulance and some men to carry his chair up the stairs into the chapel, I am sure he would. Think nothing less then being hooked up to machines would keep him from his grandson's wedding
The queen mother had the same operation at the same age, and remained active after. No reason to think Philip will suddenly become a recluse and bed ridden, unless god forbid something horrible happens.
By BBC royal correspondent Jonny Dymond:
When he first met the then-Princess Elizabeth, he is said to have showed off by leaping over the tennis court nets at Dartmouth Naval College.
His spin bowling was so good that the Australian cricketing legend Sir Don Bradman said he should play for England.
In the 1960s he was one of the top four polo players in Britain. When he gave up polo, he took up carriage driving.
And all the while he encouraged others to lead a sporting and active life, as president of the National Playing Fields Association, a patron of Outward Bound and through the establishment of the Duke of Edinburgh's Award scheme.
Much of that activity has come to an end as age has taken its toll. The duke is 96. But in early March he was seen carriage driving at Windsor.
Incapacity will be a torment to a man so used to activity. His doctors will want him up and about as soon as possible after the operation, to kick-start the healing process. They will find it difficult to restrain him.
A hip replacement is major surgery so is usually only recommended if other treatments, such as physiotherapy or steroid injections have not helped alleviate pain or improve mobility.
It is carried out under a general anaesthetic or an epidural, with the surgeon making an incision into the hip, removing the damaged joint and replacing it with an artificial joint made of a metal alloy or ceramic.
Patients have to be well enough to cope with a major operation which lasts between 60 and 90 minutes, and the rehabilitation afterwards.
Rehabilitation can be demanding and requires commitment, with patients having to walk with crutches for the first four to six weeks after the operation.
Exercise programmes are often issues to help patients regain and then improve the use of the new hip.
Most people are back to normal within two to three months but it can take up to a year before patients experience the full benefits of the new hip.
Re: walking on crutches for weeks:Articles from the BBC and Sky News:... Royal Correspondents outside the hospital.