Britain's Queen Elizabeth decided on Wednesday to rest for the next few days on advice from doctors and cancelled a planned visit to Northern Ireland, Buckingham Palace said, Reuters reports.

The palace did not say why the queen had been told to rest, though it said the 95-year-old monarch was in "good spirits" and looking forward to visiting Northern Ireland in the future.

The queen spent Tuesday night hosting a drinks reception at Windsor Castle for billionaire business leaders such as Bill Gates after Prime Minister Boris Johnson convened a green investment conference

A source said the queen's decision was not related to COVID. She is resting at Windsor Castle, the world's oldest inhabited castle.