Queen Elizabeth II spent Wednesday night at a hospital while undergoing "preliminary investigations," said a Buckingham palace spokesperson.
"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," the spokesperson's statement read.
A source with Buckingham Palace told CNN that the hospital visit was not initially announced because it was going to be a short stay, and noted that the Queen is entitled to medical privacy. The Queen was reportedly back undertaking light duties on Thursday afternoon.
She is the world's longest-reigning monarch, presiding over the nation for almost seven decades.
Earlier this week, the Queen turned down a magazine's attempt to award her the title "Oldie of the Year," saying she "felt too young at heart."
"Her Majesty believes you are as old as you feel, as such The Queen does not believe she meets the relevant criteria to be able to accept, and hopes you will find a more worthy recipient," read a letter from her assistant private secretary, Tom Laing-Baker, to the magazine.
Meanwhile, Queen Elizabeth II has cancelled her trip to Northern Ireland and has “reluctantly accepted medical advice to rest for the next few days,” said Buckingham Palace.
She is still expected to attend the COP26 climate conference in Glasgow, Scotland, later this month.
(At The Quint, we are answerable only to our audience. Play an active role in shaping our journalism by becoming a member. Because the truth is worth it.)