Britain's Queen Elizabeth spent a night in hospital for what Buckingham Palace called "initial checks", but returned to Windsor Castle on Thursday in good spirits.
The Queen, 95, canceled an official trip to Northern Ireland on Wednesday, as the palace said her medical team had advised her to rest and that it was not a case of Covid-19.
"Following medical advice to rest for days, the Queen attended hospital on Wednesday afternoon for initial checks, and returned to Windsor Castle at lunchtime today (Thursday) in high spirits," the palace said in a statement.
A royal source stated that the Queen remained in the hospital, and that her medical team had taken a precautionary approach.
The source added that she returned to her office to work on Thursday afternoon, and did some light tasks.
Queen Elizabeth spent Tuesday evening hosting a group of prominent business leaders, including Bill Gates, at Windsor Castle, after Prime Minister Boris Johnson convened a green investment conference ahead of the climate summit.
The Queen - the world's largest and longest-reigning monarch - appeared in good health at the time, and greeted the guests with a smile.
Queen Elizabeth II recently participated in a number of public activities, after spending successive periods of stone at Windsor Palace near London, although many expected her to stay away from such activities after the death of her husband Philip last April.
Last week, the Queen was seen walking with a cane, her first public appearance in this way since 2004.