Queen Elizabeth II's husband Prince Philip has been admitted to hospital for treatment for a chest infection, Buckingham Palace said on Friday, but he was reported to be continuing to work.
The 86-year-old is understood to be sitting up and dealing with correspondence after being admitted to the private King Edward VII Hospital in central London, media reports said.
"His Royal Highness's programme of engagements for the weekend have been cancelled," said a Palace spokeswoman, adding that he had been taken to hospital for "assessment and treatment for a chest infection."
His diary engagements for next week have not been cancelled, she added.
Prince Philip was last seen on high-profile duty during a state visit by French President Nicolas Sarkozy last month, but reportedly missed a memorial service for Everest conqueror Sir Edmund Hillary on Wednesday.
Last October, it was reported that Philip had had a secret heart condition for the last 15 years. The Evening Standard also said he had suffered a recent bout of ill-health which caused concern among the royal family.
Born Prince Philippos of Greece and Denmark in June 1921, he is well-known for his robust personality and sometimes embarrassing off-the-cuff remarks.
He has enjoyed good health into his 70s and 80s, keeping a trim figure notably by taking part in carriage driving competitions, a typical royal pursuit.
Prince Philip has suffered arthritis in his right wrist from playing polo – a sport which, as a younger man, landed him with a broken ankle or needed stitches on a number of occasions. He also swims regularly.
When he turned 70, a royal physician described him as "astonishingly fit for a man of his age".
On Monday he is scheduled to attend two engagements at Windsor Castle, the queen's residence southwest of London.
Next Thursday, he is due to accompany the queen to an engagement at Britannia Royal Naval College in Dartmouth, south-west England.
Over the last six months, Philip's name has been in the spotlight notably at the inquest into the death of Princess Diana and her boyfriend Dodi Fayed.
Fayed's father, the multi-millionaire boss of top London store Harrods Mohammed Al-Fayed, has accused him of having ordered her death as part of a plot to prevent her marrying a Muslim and having his baby. (AFP)
UK's Prince Philip hospitalised with chest infection: Palace