The coronavirus threat was made alarmingly vivid Wednesday to millions of people in the United Kingdom with the news that Prince Charles has contracted the virus, albeit in mild form.

Already reeling from anxiety and uncertainty, this announcement from Clarence House suddenly brought home to the British the stakes for the future as COVID-19 continues its seemingly inexorable march around the globe.

Americans might wonder: Why is this such a big deal? However imperfect the analogy, they should think of this in the same way they would greet news that the vice president of the United States had tested positive.

The Prince of Wales, 71, is Britain's future head of state as King Charles III. He is first in line after his mother, Queen Elizabeth II, who turns 94 next month. If something were to happen to both of them, his elder son, Prince William, Duke of Cambridge, 37, would become King William V. 

"It is unequivocally important," says Sally Bedell Smith, the acclaimed American biographer of multiple royals, including Charles. "It’s a very big deal because Charles is the heir apparent and if anything happens to him, then his son will become the heir apparent and will be next in line."

Even though the monarch has no overt power in a constitutional monarchy, Smith says the British monarch is still crucial to the functioning of the British government, as the head of the military, for instance. If the heir to the crown is suddenly threatened, it's unsettling to say the least, Smith says.

Moreover, millions of Brits have known no other heir than Prince Charles, the longest-serving Prince of Wales in British history.  

"The British have a relationship with Prince Charles, most of us do not remember another heir," says Victoria Arbiter, the British-born CNN royal commentator, who is the daughter of one of the queen's former press secretaries. "Prince Charles has been in all our living rooms, he was just always there, he's part of the fabric of British life."

True, there have always been critics who dreamed that the crown would bypass Charles and go directly to William, at least since Charles' messy divorce from William's mother, the late Princess Diana, in 1996, followed by her shocking death in a Paris car wreck in 1997. 

But a constitutional monarchy doesn't work like that in the absence of revolution or tragedy. So it's no surprise the British would be worried: Suddenly, this scenario seems a little less far-fetched.

And it happens to come just as Charles' standing among his future subjects has soared, as his years of filling in for his mother, his prodigious charity work and his obvious happiness with second wife, Duchess Camilla of Cornwall, 72, have improved his public profile. (She has tested negative and is with Charles in isolation at Birkhall, his estate at Balmoral in Scotland.)

"In recent years, he's become the nation's favorite granddad, and people are grasping now that he was preaching about climate change, preaching about religious tolerance over 40 years ago," says Arbiter.

"Yes, he was ridiculed, yes, he was loathed at times. But his popularity has skyrocketed in recent years. People were thrilled to see him escort Meghan (Markle) down the aisle at (her wedding to Prince Harry in 2018), so from a huge number of people, there’s more understanding of him now." 

Of course, he still has critics, including those who detest the monarchy in general. They made their views known on the Charles news promptly. 

"Can all journalists please not repeat the lie that Charles met the criteria for testing. He didn’t. We wish him well, but this is a national crisis in which we all have a stake and in which we all risk losing loved ones. Now is the time for equal access to medicine. No exceptions," tweeted the main republican organization, Republic. 

So far, Charles is said to be experiencing mild symptoms of coronavirus. Smith says he's in remarkably good shape for a man his age.

"He's as healthy a 71-year-old as you could find," she said. "He's very fit, he walks a lot, he's outdoors a lot, he exercises regularly and eats extremely well, drinks moderately so his immune system should be fairly robust."

Camilla might be more vulnerable to illness, Smith said, as a former heavy smoker.

"We're told it's unlikely to escalate further and we all hope that is the case," Arbiter says. "When you see a famous figure or a royal get this virus, it brings home to everyone how we are all vulnerable no matter who you are."

Besides worry over Charles, attention naturally turns to the queen, who has been in good health generally, and her ailing husband, Prince Philip, who will be 99 in June.

Both have been at Windsor Castle since last Thursday; she moved there from Buckingham Palace a week ahead of her usual Easter routine due to the virus. He was flown there from the royal Sandringham estate in Norfolk, where he has been living mostly since he retired in 2017.

Buckingham Palace has declined to say whether either had been tested.

Charles was last in the company of the queen about two weeks ago.

“Her Majesty The Queen remains in good health," the palace said in a statement. "The Queen last saw the Prince of Wales briefly after the investiture on the morning of the 12th March and is following all the appropriate advice with regard to her welfare.”

At the March 9 Commonwealth Day service at Westminster Abbey, Charles was seen greeting people with the namaste gesture, hands together and a slight bow, instead of shaking hands. Younger royals were seen greeting people with elbow bumps.

He also was seen on March 10 sitting across a table at a charity event with Prince Albert II of Monaco, who announced last week that he, too, has tested positive for coronavirus.

If nothing else, the coronavirus news has cast a new perspective on the recent upheaval in Britain over Prince Harry and Duchess Meghan of Sussex's decision to step down as senior working royals and move to Canada to become financially independent free royals.

All that outrage and recrimination arising from "Megxit," as the tabloids called it, "vanishes into insignificance," says Smith. 

"Whatever they planned to do with their life, and I wish them well with their non-royal life, is irrelevant right now," Smith says. "What matters is Will and (Duchess) Kate and I expect they are doing what they need to do, following all advice. 

"He is more than ready for whatever fate brings them: He is very well prepared."