LONDON — Queen Elizabeth II spent a night in the hospital for the first time in eight years before returning to her royal residence at Windsor Castle Thursday.

       In a statement, Buckingham Palace said that the monarch, 95, was admitted Wednesday afternoon “for some preliminary investigations."

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       “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.

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

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       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.

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       The official also said that on Thursday afternoon, the queen returned to her desk to undertake light duties. She is currently residing at Windsor Castle.

       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.

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       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.

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

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       Before that, she was admitted to the hospital for surgery in 2003, when she had an operation “to remove torn cartilage in her right knee and lesions from her face,” The Guardian newspaper reported at the time.

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       On both occasions, she was treated at London’s King Edward VII hospital, a private hospital favored by royals.

       Jennifer Hassan contributed reporting from London.

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