The Duke of Edinburgh is known for his active lifestyle and has generally enjoyed good health well into his later years.
As his age has advanced beyond 90, Philip has faced a number of scares.
Abdominal surgery, bladder infections and a blocked coronary artery have seen him admitted to hospital on a number of occasions.
The first public acknowledgement of his advancing years came as he was preparing to turn 90 when he stepped down as president or patron of more than a dozen organisations ahead of his milestone birthday.
In October 2011, the Duke pulled out of an overnight stay in Italy because of a cold - shortly after a busy 11-day official royal tour to Australia.
Just weeks later the Duke, at the age of 90, was rushed to hospital by helicopter from Sandringham after suffering chest pains as the royal family were preparing for Christmas.
In the serious health scare, he was treated for a blocked coronary artery at Papworth Hospital in Cambridgeshire and underwent a minimally invasive procedure of coronary stenting, and spent Christmas Day and Boxing Day in hospital.
A few days after being discharged, he appeared in good health as he attended the annual New Year's Day church service at Sandringham, making the 400m trip from the main house on foot.
In the middle of the Queen's Diamond Jubilee celebrations in June 2012, the Duke was forced to miss the majority of the festivities after falling ill with a bladder infection.
He had taken part in the Jubilee river pageant in extremely wet and windy conditions the day before.
Philip was released from hospital the day before his 91st birthday. Asked if he was feeling better as he was leaving, he quipped: "Well, I wouldn't be coming out if I wasn't."
In August 2012, he spent five nights at the Aberdeen Royal Infirmary - again for a bladder infection - after being rushed to hospital during the royals' annual summer break at Balmoral in Aberdeenshire.
On June 6 2013, Buckingham Palace announced that he had been admitted to hospital for an exploratory operation on his abdomen and was expected to stay in the London Clinic for up to two weeks.
He underwent surgery under general anaesthetic the next day and the Palace said he was progressing satisfactorily and that the results would be analysed and he would spend two months convalescing.
Philip spent his 92nd birthday in hospital, when he was visited by his youngest son, the Earl of Wessex, and then the Queen.
He recuperated at Sandringham and it was nearly two months before he was next seen in public, carrying out his first official engagement since his surgery by travelling to Scotland on August 12 2013 to hand out medals at the Royal Society of Edinburgh.
He finally met his new great-grandson, Prince George, in mid-September after the Duke and Duchess of Cambridge headed to Balmoral for a private holiday when the baby was eight weeks old.
In May 2014, the duke had a "minor procedure" carried out on his right hand at Buckingham Palace and was seen wearing a bandage to protect it.
He was seen wearing hearing aids for the first time at a Palace reception on October 28 2014, when he was 93.
Just ahead of his 95th birthday in June 2016, he pulled out of the Battle of Jutland anniversary events following medical advice, with his son-in-law, Vice-Admiral Sir Tim Laurence, saying he had a "minor ailment".
Yet the Queen's official 90th birthday celebrations in June 2016 saw Philip join the monarch throughout a busy few days of festivities, from a service of thanksgiving to Trooping the Colour and a street party in The Mall.
Both the Queen and the duke fell ill with heavy colds before Christmas in 2016, forcing them to delay their trip to Sandringham by a day.
But while the Queen was not well enough to attend the Christmas Day church service or the New Year's Day one, Philip went to both.
The Duke finally retired from public duties in 2017, but the decision was not made for medical reasons.
Philip simply wanted to enjoy more of his leisure time.
Just a few days after Buckingham Palace announced his retirement, the duke, then 95, was out and about carriage driving at the Royal Windsor Horse Show.
He turned 96 in June 2017 and a week later helped the Queen celebrate her official 91st birthday at the annual Trooping the Colour parade.
On June 20 2017, he spent the day at Royal Ascot, where temperatures were so sweltering that the dress code in the Royal Enclosure was relaxed for the first time.
But that evening, Philip was admitted to King Edward VII Hospital in London as a precautionary measure, for treatment for an infection arising from a pre-existing condition.
He missed the State Opening of Parliament the next day, when the Prince of Wales stepped in to accompany the Queen.
On his final official engagement on August 2 2017, as he retired from public duties, the duke strode with ease around the forecourt of Buckingham Palace in the pouring rain, meeting Royal Marines.
He made an appearance at the Royal Albert Hall for the Festival of Remembrance in November 2017, and then the next day at the Cenotaph as the Queen watched from a balcony for the first time rather than laying a wreath.
Concerns were expressed for Philip's health when he appeared to lean against a pillar for support while standing during the Whitehall service.
But a week later he was carriage driving at Windsor on the day of his platinum wedding anniversary, and he and the Queen celebrated in the evening with a party for more than 100 family and friends.
On March 22 2018, Philip was said to have pulled out of an official engagement with the Queen and Duke of York, marking Andrew's new role as Colonel of the Grenadier Guards, because he was under the weather.
He missed the Maundy Thursday service with the Queen on March 29 because of a problem with his hip, and also did not attend church on Easter Sunday.
The Duke was admitted to hospital on Tuesday, ahead of a planned operation on his hip on Wednesday.