Andrew Parker Bowles has caught coronavirus, sparking new fears for the health of the royals.
The Duchess of Cornwall's 80-year-old ex-husband picked up the infection at the Cheltenham Festival two weeks ago, and hundreds of racegoers have also reported symptoms.
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At the four-day event, which controversially went ahead just before the Government lockdown, the former army officer was seen kissing the Princess Royal and her daughter Zara Phillips was photographed draped over his shoulder.
Anne, 69, who was seen wiping her nose with a handkerchief and appeared to have a cold, dated Parker Bowles in the early 1970s and they have remained close friends ever since.
The former Silver Stick-in-waiting to the Queen is one of Zara's godparents.
Brigadier Parker Bowles told the Daily Telegraph: "I probably got it on the Wednesday or Friday I attended Cheltenham.
"I've felt pretty bloody awful with it. It's better in the mornings and gets worse as the day goes on.
"I've had a bad cough and I've been very lethargic. I'm sleeping twice as long as normal."
Asked whether, in hindsight, the Festival in Gloucestershire should have gone ahead from March 10 to 13, he added: "To be honest it was optional whether we went. At the time the Underground was running full of people. You can't blame Cheltenham. To be fair, attendance was 10 per cent down but I do know quite a few people who picked it up there."
Although the Brigadier admitted he mixed with royals including Anne and Zara, he said he was told he wouldn't be contagious until the following Monday, March 16.
At Cheltenham Zara's husband, former World Cup winning rugby star Mike Tindall said: "Do I think cancelling everything will solve it? I'm not entirely sure."
He urged punters to "keep calm and carry on."
A source close to Peter and Autumn Phillips, who also attended the race meeting said they were feeling "fine", adding that Zara and Mike were not showing any symptoms either.
The source added: "Pete saw his mother yesterday - obviously from a distance, and she is fine too."
Although Peter and Autumn announced their divorce in February, the couple are continuing to live together on Anne's Gatcombe estate with their daughters Savannah, 9 and 8-year-old Isla.
"They are all getting on with it," added the source. "They are in the same situation as everyone else - living in close proximity and making the best of it."
Zara, Mike and their daughters Mia, 6 and 1-year-old Lena also live on the 283ha estate near Minchinhampton.
Andrew Parker Bowles married Camilla in 1973 while Prince Charles, who had met her two years earlier, was away at sea in the Royal Navy.
But by the end of the decade Charles had begun to pine for the great love of his life.
When Charles's marriage to Diana, the Princess of Wales began to fall apart in the mid 1980s, he resumed his affair with Camilla and Andrew became known in society circles as the man who "laid down his wife for his country."
He and Camilla divorced in 1995, paving the way for Charles to marry Camilla a decade later.
Andrew married Rosemary Pitman, his mistress, in 1996 but she died of cancer in 2010.
Andrew, whose parents were best friends with the Queen Mother, still escorts his old flame Anne every day to study the horses at Royal Ascot, and they remain close.
Camilla and Andrew remain good friends and see each other at frequent family gatherings.
She attended his 80th birthday party last December.
The Duchess, who married Charles in 2005, tested negative for Covid-19 at Birkhall in Scotland after Charles tested positive. He came out of self-isolation on Monday, having spent seven days apart from his wife at the bolthole on the Queen's Balmoral estate.
A Buckingham Palace footman who walks the Queen's corgis has also tested positive, along with the heir to the throne.