The monarch, 95, is experiencing mild cold-like symptoms and expects to continue light duties at Windsor this week, the palace said.

She is understood to be triple vaccinated.

COVID news live: Messages of support pour in for Queen

The Queen was in direct contact with Prince Charles the week the heir to the throne tested positive for COVID for the second time.

Others at Windsor are understood to have contracted COVID.

Sky's royal correspondent Rhiannon Mills said: "I understand that a number of cases have been diagnosed within the Windsor Castle team.

"So clearly, those around her have had COVID, she's now contracted it."

'Mild cold-like symptoms'

The announcement was made just a few weeks after the Queen, Britain's longest-reigning monarch, reached her historic Platinum Jubilee of 70 years on the throne.

A statement by Buckingham Palace said: "Buckingham Palace confirm that The Queen has today tested positive for Covid.

"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."

The Royal Household has its own royal physicians and the Queen's doctors will be on hand to take care of and monitor her health.

Professor Sir Huw Thomas, head of the Medical Household and Physician to the Queen, is expected to be in charge.

The Queen is believed to have spent time with Prince Charles on 8 February at Windsor Castle - a few days later he tested positive for the virus but made a quick recovery to full health. His wife, the Duchess of Cornwall also tested positive.

Queen 'no lover of fuss'

Sky News royal commentator Alastair Bruce said: "The Queen is no lover of fuss."

He continued: "She's in an environment where she can be very well looked after.

"She's aware that an enormous number of people, particularly of her age, have been vulnerable at this time, of getting Covid and she will take the advice that she's given, but she's pretty stalwart."

"I think the Queen's always been aware that one day she would get it," he added.

"It's amazing in a sense that she hasn't received it until now, and it underscores quite how careful the royal households have been with her. For a very feisty and determined lady of her mid-90s, she is more than ready to deal with what she faces."

Messages of support pour in

Prime Minister Boris Johnson tweeted: "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."

The chair of the Conservatives and leader of the Labour party were also among those to send well-wishes to the Queen.

Sir Keir Starmer said: "On behalf of myself and the whole of @UKLabour, wishing Her Majesty The Queen good health and a speedy recovery. Get well soon, Ma'am."

MP Oliver Dowden tweeted: "Wishing Her Majesty the Queen a swift recovery."

London Mayor Sadiq Khan added: "The commitment Her Majesty the Queen has shown to our country continues to be unwavering.

"Wishing her a swift and safe recovery from COVID-19."

'HMS Bubble'

She spent much of the pandemic in the safety of Windsor Castle, protected in 'HMS Bubble' - the nickname given to her reduced household of dedicated staff.

She has served as a symbol of stability throughout the pandemic, delivering two rare televised addresses to the nation weeks apart.

She reassured the country that the virus would be overcome, telling those in isolation: "We will meet again."

However, the COVID diagnosis will cause concern, given the Queen's advanced age and her health scares in recent months.

In October, she was pictured using a walking stick at as Westminster Abbey service - believed to be the first time she has used one at a major public event.

She has been on doctors' orders to rest since mid-October when she cancelled a run of engagements and spent a night in hospital undergoing preliminary tests.

She was unable to attend the Cenotaph on Remembrance Sunday after spraining her back.

Speaking in December, Prince Charles said of her health: "Once you get to 95, it's not quite as easy as it used to be. It's bad enough at 73."

The monarch carried out her first major public engagement for more than three months on Saturday, 5 February, the eve of her Jubilee when she met charity workers at Sandringham House and cut a celebratory cake.

Latest monarch to catch COVID

Over Christmas, the Queen cancelled her annual family gathering at her Norfolk estate amid rising Omicron cases in the UK.

It was the Queen's first Christmas period without the Duke of Edinburgh, her husband of more than 73 years, who died on 9 April last year. She was forced to sit alone during his funeral, due to ongoing pandemic restrictions.

She returned to Windsor in early February.

In recent months she has been setting her affairs in order, using her Jubilee message to endorse her daughter-in-law the Duchess of Cornwall, once a royal mistress, to be Queen Camilla and crowned at Charles's side when he one day becomes King.

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She has become the latest monarch from around the world to catch COVID.

Queen Margrethe of Denmark, 82, and Spain's King Felipe VI, 54, both tested positive for the illness on February 9.