Queen Elizabeth II resumed public duties on Tuesday for the first time since spending a night in hospital last week, holding video calls with incoming ambassadors.
The 95-year-old monarch's overnight hospital stay, which royal officials said was for practical reasons following "some preliminary investigations", has raised fears over her health, given her age.
She has also been seen using a walking stick for the first time at a major public event this month.
The Queen, who is currently living at Windsor Castle, held video calls to receive new ambassadors from South Korea and Switzerland, Buckingham Palace said in a statement Tuesday.
She was shown smiling as she spoke on a screen, wearing a yellow dress and pearls.
Her last public event was a busy Windsor Castle reception for attendees of the government's global investment summit on October 19.
Doctors subsequently ordered her to rest and she cancelled a visit to Northern Ireland later in the week.
She then went to King Edward VII's Hospital in London for tests Wednesday and stayed overnight.
It was her first hospital stay since 2013.
The Sunday Times quoted a source close to the Queen as saying "she is knackered" after attempting to keep busy following the death of her husband Prince Philip in April.
Sources told the paper the Queen has a "constant flow of lunches and dinners with family and friends" because she does not want to eat alone.
The Sunday Telegraph reported this month that the monarch is determined to stay well for her Platinum Jubilee next year.
The paper said she had recently been advised by doctors to give up drinking her regular tipples -- gin and Dubonnet before lunch, and gin and vermouth before dinner.
The head of state, who has been on the throne since 1952 and is Britain's longest-serving monarch, is due to attend the UN climate summit next week in Glasgow.
The Sunday Times reported that she is "saving her energy" for the event. Prince Charles, Prince William and other senior royals are all due to attend as well.
