Queen Elizabeth II tested positive on Sunday for Covid-19 but aides said her symptoms were "mild", as politicians wished Britain's longest-serving monarch a rapid recovery in her 70th year on the throne.
In what is meant to be a banner year of Platinum Jubilee celebrations, the news comes at a stressful time for the 95-year-old queen with scandals stalking her two eldest sons, Charles and Andrew.
It is also ill-timed for the UK government, in a week when embattled Prime Minister Boris Johnson is expected to declare a victory of sorts over the pandemic by announcing the scrapping of remaining legal restrictions in England.
The queen's heir Prince Charles, 73, tested positive for a second time for the coronavirus on February 10, two days after meeting his mother at Windsor Castle, west of London.
The queen -- who is believed to be triple-vaccinated -- resumed in-person audiences at the castle last week, but complained to one attendee of suffering from stiffness and was photographed holding a walking stick.
Announcing her first positive test, a Buckingham Palace statement said: "Her Majesty is experiencing mild cold-like symptoms but expects to continue light duties at Windsor over the coming week.
"She will continue to receive medical attention and will follow all the appropriate guidelines."
It issued a later statement in which the monarch sent her "warmest congratulations" to the British women's and men's curling teams, after they won gold and silver medals respectively at the Beijing Winter Olympics.
"I'm sure I speak for everyone in wishing Her Majesty The Queen a swift recovery from Covid and a rapid return to vibrant good health," Johnson tweeted, as members of his cabinet sent their own best wishes.
India's Prime Minister Narendra Modi also shared Johnson's tweet, adding, "I wish Her Majesty Queen Elizabeth a speedy recovery and pray for her good health."
Keir Starmer, leader of the main opposition Labour party, tweeted: "Get well soon, Ma'am."
'Symbol of the nation'
Among well-wishers gathered outside Buckingham Palace in London, cancer scientist Pasquale Morese said it was "sad" news.
"She's a symbol of the nation," he said. "She's boosted and everything, so she should be alright, hopefully."
With the infection coming two months before the queen turns 96, royal expert Richard Fitzwilliams said: "There will be concerns because of her age, no doubt about that.
"But the queen by nature is stoic. I think she's someone who looks at things in a very, very positive way," he told AFP, anticipating "reasonably regular updates" from the palace.
Queen Elizabeth has generally enjoyed robust health over her long life, but an unexplained issue saw her spend a night in hospital last October.
Nationwide celebrations to mark her Platinum Jubilee are due to be held in June, after she marked 70 years on the throne on February 6.
The Covid scare comes with the royal family mired in difficulties, including tensions with Charles's second son Prince Harry, who now lives in California with his wife Meghan.
'Feisty and determined lady'
Prince Andrew settled a sexual assault civil lawsuit in the United States last week, reportedly for 12 million pounds ($16.3 million, 14.3 million euros) -- which reports say the queen will partly fund.
Meanwhile police in London are investigating claims that a Saudi tycoon was offered UK honours in return for donations to Charles's charitable foundation.
The queen, whose husband Prince Philip died aged 99 last April, has spent much of the coronavirus pandemic at Windsor Castle, with a reduced number of household staff dubbed "HMS Bubble".
Respecting the government's rules on Covid distancing at the time, she sat alone at Philip's funeral, while Johnson and his staff are under police investigation for apparent breaches of the rules during lockdown parties in Downing Street.
With the Omicron wave apparently under control, the government is expected to press ahead with an announcement Monday lifting pandemic legislation in England.
The optics have become "a little bit tricky" given the queen's illness, Conservative MP Caroline Nokes told Times Radio.
But speaking on Sky News, royal commentator Alastair Bruce said the queen "would not want anyone to change any decisions on the basis of her state of health".
"I think for a very feisty and determined lady of her mid-90s, she is more than ready to deal with what she faces," he added.
