Britain's Prince Philip has been taken to hospital in London with a bladder infection.
The 90-year-old Duke of Edinburgh missed the Diamond Jubillee concert taking place outside Buckingham Palace this evening.
A spokesman at Buckingham Palace said the Duke was hospitalised as a "precautionary measure" and would remain under observation for a few days.
The new health scare comes less than six months after the outspoken British royal patriarch suffered chest pains.
He had to undergo a medical procedure to treat a blocked coronary artery.
Queen Elizabeth lit the centrepiece in a chain of 4,200 beacons spanning the Commonwealth following a star-studded concert in front of Buckingham Palace featuring Elton John, Tom Jones, Paul McCartney, Shirley Bassey and Stevie Wonder.
She will without her husband during a ceremonial carriage procession through the streets of London tomorrow that will round off the jubilee festivities.
Prince Philip, the longest serving royal consort in British history, will turn 91 next Sunday.
He appeared in good health on Sunday as he travelled on the royal barge in chilly conditions during a 1,000-boat river pageant for the jubilee.
The former Royal Navy commander was seen saluting to passing boats, smiling and waving during the pageant.
He was also in animated form at the Epsom Derby races on Saturday, waving his top hat to the crowds as he arrived and pointing things out from the royal balcony to his grand-daughters, Princesses Beatrice and Eugenie.