London (CNN) Prince Charles, Queen Elizabeth II's son and the heir to the British throne, has tested positive for coronavirus and is now self-isolating in Scotland, his office announced Wednesday.

The Prince of Wales is only displaying mild symptoms and is otherwise in good health, Clarence House said in a statement. It is unknown how the 71-year-old caught the virus because of his recent busy schedule of public events.

The Queen, 93, remains in "good health" and is "following all the appropriate advice with regard to her welfare," a Buckingham Palace spokesperson said Wednesday.

The monarch last saw Prince Charles briefly after an investiture ceremony for public awards at the palace in London on March 12. Charles has been advised he was contagious from March 13, a royal source told CNN.

It is unclear why Prince Charles was advised he was not contagious earlier. The coronavirus incubation period -- the amount of time from exposure to symptoms -- is usually around five or six days, with a maximum of around 12 days, according to research published this month in the medical journal Annals of Internal Medicine.

According to a royal source, Prince Charles started showing symptoms last weekend, meaning he could have been exposed before he saw the Queen on March 12.

He was tested on Monday and received the results on Tuesday, the source told CNN.

Prince Charles's office at Clarence House has not responded to CNN's query regarding the timeline. "It is not possible to ascertain from whom the Prince caught the virus owing to the high number of engagements he carried out in his public role during recent weeks," his office said earlier.

Both Public Health England and the US Centers for Disease Control and Prevention say there are indications people could be contagious before they show symptoms. While people are probably most contagious when they are symptomatic, scientists currently cannot pinpoint exactly when people can start spreading the disease.

Following his last public event on March 12, Prince Charles has had a number of private meetings with individuals, all of whom have been made aware of the situation.

He is self-isolating at his Scottish residence of Birkhall in Aberdeenshire, on the Queen's Balmoral estate, with a small number of staff keeping separate from him, the source added. His wife Camilla, the Duchess of Cornwall, is self-isolating separately. She has been tested and does not have the virus, according to the statement from Clarence House.

The tests were carried out by the National Health Service in Aberdeenshire, where the couple met the criteria required to be tested, the statement added.

Photos: The heir apparent: Britain's Prince Charles Prince Charles poses for an official portrait in November 2008. Hide Caption 1 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles was born at Buckingham Palace in London on November 14, 1948. His mother was Princess Elizabeth at the time. Hide Caption 2 of 53 Photos: The heir apparent: Britain's Prince Charles Princess Elizabeth and her husband, Prince Philip, sit on a lawn with their children Prince Charles and Princess Anne in August 1951. Hide Caption 3 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles attends his mother's coronation in 1953 with his grandmother, left, and his aunt Margaret. Hide Caption 4 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles, right, shakes hands with Sir Gerald Creasy, the governor of Malta, as he and the rest of the royal family visit Malta in May 1954. Hide Caption 5 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles rides with his mother and grandmother as they travel to Westminster Abbey for the wedding of Princess Margaret in May 1960. Hide Caption 6 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles prepares for takeoff during a flying lesson in 1968. In 1971, he earned his wings as a jet pilot and joined the Royal Navy. Hide Caption 7 of 53 Photos: The heir apparent: Britain's Prince Charles Queen Elizabeth II presents Prince Charles to the people of Wales after his investiture as the Prince of Wales in July 1969. Hide Caption 8 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles walks at Trinity College, Cambridge, where he earned a bachelor's degree in 1970. He was the first royal heir to earn a university degree. Hide Caption 9 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles, left, rides go-carts with his brother Prince Edward and his sister, Princess Anne, circa 1969. Hide Caption 10 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles meets US President Richard Nixon during a private visit to Washington in July 1970. Hide Caption 11 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles attends a conference with his father in November 1970. Hide Caption 12 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles goes on a safari in Kenya in February 1971. Hide Caption 13 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles prepares to fire a bazooka while visiting military barracks in West Berlin in October 1972. Hide Caption 14 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles fishes with a wooden spear circa 1975. Hide Caption 15 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles poses for sculptor David McFall in December 1975. Hide Caption 16 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles smokes a peace pipe during a visit to Canada in July 1977. Hide Caption 17 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles rides a horse during an equestrian event in Cirencester, England, in April 1978. Hide Caption 18 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles, as colonel-in-chief, visits the Cheshire Regiment in Canterbury, England, in November 1978. He served in the Royal Navy from 1971 to 1976, and in 2012 his mother appointed him honorary five-star ranks in the navy, army and air force. Hide Caption 19 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles and Camilla Parker-Bowles are seen together circa 1979. They dated in the 70s and would eventually marry in 2005. It was the second marriage for both. Their first marriages ended in divorce. Hide Caption 20 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles poses outside the Taj Mahal in India in 1980. Hide Caption 21 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles kisses his first wife, Lady Diana Spencer, on the balcony of Buckingham Palace in July 1981. Their wedding ceremony was televised. Hide Caption 22 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles and Princess Diana leave a London hospital with their first child, William, in July 1982. Hide Caption 23 of 53 Photos: The heir apparent: Britain's Prince Charles Charles and Diana dance together at a formal event. Hide Caption 24 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles shares a playful pie in the face while visiting a community center in Manchester, England, in December 1983. Hide Caption 25 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles walks with natives on a visit to Papua New Guinea in 1984. Hide Caption 26 of 53 Photos: The heir apparent: Britain's Prince Charles Charles and Diana sit together in Toronto during a royal tour in October 1991. A year later, they were separated. Charles' affair with Camilla Parker-Bowles became public in 1993. Hide Caption 27 of 53 Photos: The heir apparent: Britain's Prince Charles Charles, Diana and their two sons, William and Harry, gather for V-J Day commemorations in London in August 1995. The couple divorced one year later. Hide Caption 28 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles visits a mosque in London in March 1996. Hide Caption 29 of 53 Photos: The heir apparent: Britain's Prince Charles South African President Nelson Mandela talks with Prince Charles in London in July 1996. Hide Caption 30 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles poses with the Spice Girls in 1997. Hide Caption 31 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles and his sons spend time together at the Balmoral Castle estate in Balmoral, Scotland, in August 1997. Hide Caption 32 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles, second from right, and Princess Diana's two sisters meet in Paris after Diana was killed in a car crash there in August 1997. She was 36 years old. Hide Caption 33 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles and his sons follow Diana's hearse in London in September 1997. Hide Caption 34 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles stands beside his grandmother's coffin while it lies in state at Westminster Hall in London in April 2002. Hide Caption 35 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles carries a specially painted football through the streets of Ashbourne, England, in March 2003. Hide Caption 36 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles watches a parachute regiment during a D-Day re-enactment in Ranville, France, in June 2004. Hide Caption 37 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles married Camilla Parker-Bowles in April 2005. Hide Caption 38 of 53 Photos: The heir apparent: Britain's Prince Charles Queen Elizabeth II presents Prince Charles with the Royal Horticultural Society's Victoria Medal of Honor during a visit to the Chelsea Flower Show in London in May 2009. Hide Caption 39 of 53 Photos: The heir apparent: Britain's Prince Charles Charles and Camilla were on their way to a performance at the London Palladium when their car was attacked by angry student protesters in December 2010. The students were protesting a hike in tuition fees. Hide Caption 40 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles and Queen Elizabeth II were among those on the Buckingham Palace balcony after Prince William wed Kate Middleton in April 2011. Hide Caption 41 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles reads the weather while touring BBC Scotland's headquarters in May 2012. Hide Caption 42 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles meets with US President Barack Obama in the White House Oval Office in March 2015. Hide Caption 43 of 53 Photos: The heir apparent: Britain's Prince Charles Charles and Camilla react as Zephyr, the bald-eagle mascot of the Army Air Corps, flaps his wings at the Sandringham Flower Show in July 2015. Hide Caption 44 of 53 Photos: The heir apparent: Britain's Prince Charles Members of the royal family pose for a photo at Buckingham Palace in December 2016. From left are Camilla, Duchess of Cornwall; Prince Charles; Queen Elizabeth II; Prince Philip; Prince William; and Catherine, Duchess of Cambridge. Hide Caption 45 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles visits the Italian town of Amatrice in April 2017, after an earthquake had hit. Hide Caption 46 of 53 Photos: The heir apparent: Britain's Prince Charles Charles and Camilla ride on a raft while visiting the island of Borneo in November 2017. Hide Caption 47 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles leads three cheers for his mother as the Queen celebrated her 92nd birthday at a London concert in April 2018. Hide Caption 48 of 53 Photos: The heir apparent: Britain's Prince Charles From left, Prince Charles, Prince Andrew, Duchess Camilla and Queen Elizabeth II watch a Royal Air Force flyover in July 2018. Hide Caption 49 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles accompanies his future daughter-in-law, Meghan Markle, as she is married to Prince Harry in May 2018. Hide Caption 50 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles lays a wreath at the Cenotaph in London to commemorate Remembrance Day in November 2018. It was also the 100th anniversary of the end of World War I. Hide Caption 51 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles poses with family members for an official portrait to mark his 70th birthday. He's holding his grandson Prince George as Camilla sits next to his granddaughter, Princess Charlotte. In the back row, from left, are his grandson Prince Louis; his daughter-in-law Catherine; his son Prince William; his son Prince Harry; and his daughter-in-law Meghan. Hide Caption 52 of 53 Photos: The heir apparent: Britain's Prince Charles Prince Charles speaks at an event in London in March 2020. Later that month, it was announced that he had tested positive for the novel coronavirus. A statement on March 25 said that Charles was "displaying mild symptoms but otherwise remains in good health and has been working from home throughout the last few days as usual." Hide Caption 53 of 53

Prince Charles has not been to hospital, the royal source said Wednesday, adding that he was tested because of his age and medical history. He has spoken to the Queen and to his sons William and Harry, the source said. The medical advice he has been given is that this is "unlikely to escalate into a more serious case."

Prince Charles continues work and is in "good health and indeed good spirits," the royal source told CNN.

The prince has a reputation for working hard, and meets more members of the public than virtually any other member of the royal family. His aides are now racing to determine how, when and where he contracted the virus, and with whom he may have had contact since.

Despite the Queen being in her mid-90s, it is not known whether she has been tested.

The source asked not to be named discussing the royal family's medical condition.

Last week the palace said the Queen was canceling public events "as a sensible precaution" and that she and her husband, 98-year-old Prince Philip, moved to Windsor Castle on Thursday, a week earlier than planned. She is expected to stay there beyond the Easter period.

In a statement issued by the palace as they moved to Windsor, the Queen said the world was entering "a period of great concern and uncertainty" and warned that many would need to "find new ways of staying in touch with each other and making sure that loved ones are safe." She said she and her family were ready to play their part.

Prince Charles is the eldest child of the Queen and Prince Philip, the Duke of Edinburgh. As someone over 70, he is considered to be at higher risk than average for coronavirus.

Earlier this month, his office said he was not yet self-isolating because UK government and medical advice at the time were not advising over-70s to do so.

On March 13, Prince Charles and his wife announced they were canceling their spring tour due to the escalating coronavirus pandemic. The pair had been set to visit Bosnia and Herzegovina, Cyprus and Jordan.