LONDON — Queen Elizabeth II was resting and undertaking light duties on Friday after she spent a night in the hospital for some “preliminary investigations” — causing a bit of a stir in a country glued to any reports of her health — before returning to Windsor Castle.

Britain’s 95-year-old monarch was admitted to a London hospital on Wednesday afternoon, widely assumed to be London’s King Edward VII Hospital, a private hospital favored by royals, and discharged the following day. It was her first overnight stay in a hospital in eight years.

“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 palace said.

Her stay was only revealed after Britain’s Sun newspaper broke the story late Thursday. As the only monarch the vast majority of Britons have ever known, the queen has been a reassuring presence in people’s lives and any hint of medical issues is taken very seriously.

The BBC’s royal correspondent Nicholas Witchell, who was criticized on social media for wearing a black suit and tie, told BBC Breakfast on Friday that the situation was “quite difficult to read.”

“We were led to believe on Wednesday by Buckingham Palace that the queen was resting” when she was, in fact, in the hospital, he said. “We weren’t given the complete picture then.” He added that while the palace would argue the case for medical privacy, “the problem it seems to me is that rumor and misinformation always thrives in absence of proper, accurate and trustworthy information.”

It’s not surprising that the palace didn’t issue a medical bulletin immediately. They normally don’t say anything when royals go to the hospital for checkups or tests, but they will issue statements when royals have procedures or operations, or if events are canceled, to explain the no-show. But after the Sun got a leak about the queen’s hospital stay, the palace responded.

Earlier this week, the palace did announce the queen canceled a two-day visit to Northern Ireland after accepting medical advice to rest for the next few days.

A palace official, speaking on the condition of anonymity to discuss private interactions, said that the queen had stayed in hospital overnight for practical reasons and that her medical team was taking a cautious approach.

The official on Friday said that the situation was the same as on Thursday, with the queen expecting to rest and undertake light duties. She is currently residing at her Windsor Castle home.

Her last official event was on Tuesday when she welcomed business leaders and diplomats at the castle for a government-sponsored investment summit. In a video posted on the Royal Family’s Twitter account, the queen appeared in good spirits, smiling and chatting with guests.

The queen had returned to Windsor Castle from Balmoral, the royal residence in Scotland where she spends her summers, earlier this month. Since then, she has maintained a busy schedule, traveling to Cardiff and Edinburgh to address the Welsh and Scottish parliaments and to Ascot for a day at the races. She also held several diplomatic “audiences” via video link.

Prime Minister Boris Johnson said that he understood that the queen was back at work on Friday. “I think everybody sends Her Majesty … our very, very best wishes, everybody does and certainly we have from the government,” he told reporters during a trip to a vaccination center.

“I am given to understand that actually Her Majesty is, characteristically, back at her desk at Windsor as we speak,” he said.

Robert Hardman, author of the forthcoming “Queen of Our Times,” said it was hard to know if the queen might slow down, but that there were certain “core” duties she would be loath to give up on.

“She genuinely likes doing the job,” he told The Washington Post. “The absolute core functions she’d never give up on are: talking to the prime minister once a week, opening parliament if she can, honoring the war dead every remembrance Sunday and addressing the nation at Christmas. Those are the core functions she will be keen to continue and everything else on top of that, will be subject to doctors orders and common sense.”

He added that the queen has a “real horror of letting people down,” and recalled how, years ago, she had to cancel an event at the last minute at Arsenal soccer stadium because of back trouble. A month later, the soccer club got a call from the palace inviting the squad to the palace for tea with the queen.

“If she does let people down, she hates doing it and tries to make it up to them. I have no doubt having not going to Northern Ireland this week, Northern Ireland will get a visit in due course,” he said.

The queen was last hospitalized in 2013 after displaying symptoms of gastroenteritis, which forced her to cancel her trip to Rome.

Jennifer Hassan in London contributed to this report.

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