Queen Elizabeth II was spotted at the wheel of a car at Windsor Castle on Monday, British media reported, allaying fears for her health after she skipped the UK-hosted COP26 summit on doctors' advice.
The 95-year-old was seen alone in a green Jaguar estate she uses to transport her corgis, The Sun tabloid reported, under the headline: "One is OK".
The Queen pulled out of the United Nations climate summit, where world leaders gathered in Glasgow on Monday, after a rare public admission of health problems.
Buckingham Palace said in late October that she had attended a London private hospital for undisclosed "preliminary examinations" and stayed overnight.
The Queen swiftly resumed official duties and held several audiences via video link.
But she then pulled out of an expected appearance at an evening reception for COP26 in Glasgow on Monday after "advice to rest", Buckingham Palace said.
The Palace later said she would rest for "at least" another two weeks.
Prime Minister Boris Johnson at the weekend said she was on "very good form". She is still set to deliver an a pre-recorded video address to COP26 delegates at the evening event.
Her eldest son and heir, Prince Charles, was one of the speakers on Monday, along with revered natural history broadcaster David Attenborough, who is also 95.
The royal family has spoken out repeatedly about environmental issues in recent weeks and in mid-October the Queen was overheard expressing irritation with world leaders who "talk" but "don't do" enough about climate change.
Britain's longest-reigning monarch will celebrate her Platinum jubilee next year, marking 70 years on the throne.
Until her hospital stay this month, she had participated almost daily in official engagements.
She was recently seen walking with a cane and has reportedly given up riding horses however.
The Queen's husband Prince Philip, the Duke of Edinburgh, died on April 9 aged 99, just weeks short of his 100th birthday.