|Queen Elizabeth and Prince Phillip|
The 86-year-old British monarch is being treated at a London medical facility for gastroenteritis.
The royal was admitted to King Edward VII hospital on Sunday after falling ill on Friday night.
A spokesperson for the palace said: "She was not taken into the hospital immediately after feeling the symptoms. This is simply to enable doctors to better assess her."
The queen is only expected to remain under medical supervision until Tuesday but all her official engagements this week, including her trip to Rome, will be either cancelled or postponed as she recovers from the nasty stomach bug.
The royal, who reportedly has had no visitors from her family yet, was last hospitalized for a minor knee operation almost a decade ago but her husband Prince Philip was rushed to hospital last August as a "precautionary measure" when he fell ill after spending hours on a ceremonial barge in rain and a cold wind as part of a flotilla of 1,000 vessels on the River Thames to mark her landmark Diamond Jubilee.
In December 2011 he also had a heart operation where surgeons cleared a blocked coronary artery and inserted a stent to ease the problem.