The 95-year-old monarch arrive home from the private hospital in central London in the middle of the day on Thursday and is “in good spirits”, the palace said.
The Queen had call off a visit to Northern Ireland on Wednesday.
This was sequel to medical advice given to her to rest for a few days after a busy schedule of public activities.
Prime Minister Boris Johnson declared “everybody sends Her Majesty our very very best wishes”.
He also declared he was
“given to understand that actually Her Majesty is characteristically back at her desk at Windsor as we speak”.
In a affirmation on Thursday night, Buckingham Palace said:
“Following medical advice to rest for a few days, the Queen attended hospital on Wednesday afternoon for some preparatory examination, returning to Windsor Castle at lunchtime today, and remains in good spirits.”
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The Queen travelled by car to the King Edward VII’s Hospital in Marylebone, about 19 miles (32km) from Windsor, where she was seen by experts. Heradmission is understood not to be connected to COVID-19.
The overnight stay was believed to be for viable reasons and the Queen was going through light duties back at Windsor on Thursday afternoon.
It is the first time the Queen has stayed in hospital since 2013, when she experienced signs of gastroenteritis.
The King Edward VII’s is a private hospital used by senior royals – inclusive of the Queen’s husband, the late Duke of Edinburgh, who received treatment there earlier this year.
The information on Wednesday that the Queen would have to call off a trip to Northern Ireland was always going to cause anxiety.
In spite of looking very well and happy at so many events she has attended over the past week, it cannot be out of mind that she is 95 years old.
It is a sensitive balance for the palace to release enough details about the Queen’s health to keep the public well informed and at the same time maintaining the privacy to which she is entitled.
It was for this obvious fact that the news that she had been taken to hospital for tests was not made public, till a report on the Sun newspaper’s front page forced the palace’s hand.
People will be worried,even so the reassuring guidance remains that she is in “good spirits” on her return from hospital and is well enough to take on some light duties.
It has been a busy period of official commitment for the monarch.
An official record of the Queen’s diary revealed at least 16 formal events during October, and there had been the intentions for her to start the two-day trip to Northern Ireland this week.
She was captured hosting a Global Investment Summit at Windsor Castle on Tuesday evening with Mr Johnson.
But, on Wednesday a Buckingham Palace spokesperson declared the Queen had
“reluctantly accepted medical advice to rest for the next few days”.
He said the Queen was
“disappointed that she will no longer be able to visit Northern Ireland”
– which would have included an overnight stay.
The Queen’s October engagements
The Queen started the month in Scotland, planting a tree with the Prince of Wales at the Balmoral Estate on 1 October and appearing at opening of the sixth session of the Scottish Parliament in Edinburgh the next day.
The next week, she met members of the Canadian military at Windsor Castle on 6 October and appeared at the launch of the Commonwealth Games baton relay at Buckingham Palace on 7 October.
Last week, on 12 October precisely, she also appeared at a church service to mark the centenary of The Royal British Legion at Westminster Abbey.
She after that traveled to Wales to open the sixth term of the Senedd on Thursday.
On Saturday she was back in England – and attended Champions Day at Ascot racecourse in Berkshire.
On Tuesday evening the Queen was back at Windsor Castle hosting the Global Investment Summit.
The Monarch is anticipated to lead a royal representatives to the Glasgow COP26 climate change summit in two weeks’ time.
In reported comments overheard at an event last week, she seemed to suggest she was annoyed by people who “talk” but “don’t do” when it came to preserving the environment.
Earlier this week, the Queen rejected a magazine’s award of Oldie of the Year, saying
“you are only as old as you feel”.
She “politely but firmly” turn down the award, but sent the Oldie magazine a piece of information with her “warmest best wishes”.