The Queen spent Wednesday night in hospital after cancelling a visit to Northern Ireland, Buckingham Palace has said.
The 95-year-old had been due to take part in a two-day trip, but doctors told her that she should rest for a couple of days at Windsor Castle.
However she was then admitted to hospital for “preliminary investigations”. She returned to Windsor on Thursday.
The Queen was seen by specialists at the private King Edward VII’s hospital in central London. Her admittance is understood not to have been related to coronavirus. It was her first overnight stay in hospital since 2013, when she also spent one night at the King Edward VIII, being treated for gastroenteritis.
A palace source said that a “cautious approach” had been taken by the medical team aiding her. They added that the overnight stay was for practical reasons and she was working on Thursday afternoon, undertaking “light duties”.
She was said to be disappointed not to be able to travel to Northern Ireland on Wednesday, and reluctantly heeded the advice of her doctors.
On her visit she had been due to meet local people including schoolchildren in Hillsborough, County Down, after the village was officially named Royal Hillsborough. It is the first village or town in Northern Ireland to be granted royal status.
The Queen was also planning to attend a church service in Armagh on Thursday to mark the centenary of Northern Ireland’s formation.
Last week she had been pictured using a walking stick in public for the first time at a major public event when she attended a service marking the centenary of the Royal British Legion.
Since returning from Balmoral at the beginning of October, she had hosted a major global investment summit at Windsor Castle on Tuesday evening where she was said to have been bright and cheerful. She has kept up a busy schedule of events since the death of her husband, Prins Philip, at age 99 earlier this year.
A palace spokesperson said: “Following medical advice to rest for a few days, the Queen attended hospital on Wednesday afternoon for some preliminary investigations, returning to Windsor Castle at lunchtime today, and remains in good spirits.”