Queen Elizabeth II, 95, was taken to the hospital on Wednesday for "preliminary investigations" and was released Thursday, Buckingham Palace confirmed.

"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," Buckingham Palace said in statement.

CBS News' Holly Williams reported that a royal source said the queen stayed in the hospital overnight because it was too late at night to be driven home. .

Buckingham Palace said Wednesday that she was "disappointed that she will no longer be able to visit Northern Ireland."

According to BBC News, Queen Elizabeth is expected to lead the royal delegation at the climate summit in Glasgow in two weeks.