Britain's Queen Elizabeth II was back at Windsor Castle on Friday and in good spirits after revelations that she spent the night in a London hospital earlier this week. Buckingham Palace said the 95-year-old British monarch went to the private King Edward VII's Hospital in London on Wednesday for "preliminary investigations." She returned to her Windsor Castle home at lunchtime on Thursday and was understood to be back at her desk by afternoon, undertaking light duties. The queen underwent the tests after she canceled a scheduled trip to mark 100 years since the creation of Northern Ireland, and the palace said she had "reluctantly" accepted medical advice to rest for a few days. The matter was not related to COVID-19.