Britain's 86-year-old Queen Elizabeth II spent Sunday night in hospital after being admitted for the first time in 10 years as a precautionary measure against the symptoms of gastroenteritis.
A Buckingham Palace spokesman said the monarch's planned visit to Rome this week had been called off. The British Queen hasn't made an overseas trip since October 2011.
Known for her robust health and devotion to duty, Britain's head of state rarely misses engagements.
"The Queen is being assessed at King Edward VII's Hospital in London after experiencing symptoms of gastroenteritis. As a precaution, all official engagements this week will be either postponed or cancelled," the palace spokesman said.
He added that the monarch was in "good spirits" and was otherwise in "good health".
"This is a precautionary measure," the spokesman stressed. "She was not taken into hospital immediately after feeling the symptoms. This is simply to enable doctors to better assess her."
The Queen was reported to have been well enough earlier Sunday to present an award to a member of staff for her long service and also to attend a chapel service in Windsor.
Broadcasters reported the monarch would remain in hospital under observation for about two days, and would likely be placed on a drip in order to combat dehydration.
It was also reported that she would not be taking visitors in order to minimise publicity.
Prime Minister David Cameron on Sunday issued a statement saying: "We wish the Queen well and wish her a speedy recovery."
After coming down Friday with gastroenteritis -- an infection of the stomach and bowel with symptoms commonly including vomiting, diarrhoea and dehydration -- the sovereign missed celebrations in Swansea on Saturday to mark St. David's Day, the national day of Wales.
Instead of that engagement, she had been resting at Windsor Castle, west of London, where she and her husband Prince Philip usually spend the weekend.
The queen had on Thursday presented honours to group of stars from the London 2012 Olympics, including gold-medal winning heptathlete Jessica Ennis, during a ceremony at Buckingham Palace.
While the Queen is hospitalised, Pregnant Kate, Prince William and Prince Harry are in Switzerland to attend the wedding of their friends polo player Mark Tomlinson to Olympic dressage gold medallist Laura Bechtolsheimer.
The Royal trio beamed during the ceremony and as the newly-married couple walked past them, an evidently delighted Kate threw a handful of confetti into the air.
But with the Queen in the hospital bed we hope the trio catch the next flight back home to be by her side.
The British monarch is known for her robust health and has rarely missed a royal engagement due to ill health in recent years.
She was last forced to pull out of an investiture ceremony - where she presents honours including knighthoods - in October last year due to a bad back.
The monarch also missed a visit to the British Museum in October 2011 after suffering from a cold.
In March 1993, she was forced to cancel several engagements with the flu but in the same month refused to cancel a visit to a handbag factory despite having had three stitches in her left hand after being bitten by one of her corgis.
In 2006 she suffered a strain to her back during her annual summer break at Balmoral which led to her cancelling a tour of Arsenal foootball club's new stadium.
In recent times there have been more concerns about the health of her husband, the 91-year-old Duke of Edinburgh.
In August last year he spent five nights in Aberdeen Royal Infirmary being treated for a repeat of the bladder infection which had also seen him hospitalised for five nights in June.
He spent four nights at Papworth Hospital in Cambridgeshire, eastern England, in December 2011 following a successful procedure to clear a blocked coronary artery.
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