British Media Showed Restraint on Princess Kate’s Health. It Didn’t Make a Difference.

Days before Catherine, Princess of Wales, ended the wild speculation over her absence from public life by revealing that she is battling cancer, a top royal journalist appeared on British national television and delivered a stark message to the media: Knock it off.

“I think everyone just needs to give her a little bit of space,” Roya Nikkhah, royal editor of The Sunday Times of London, said on “Good Morning Britain.” “This is a woman who’s been in the public eye since she was in her early 20s, and she’s barely put her foot wrong. I think we should all lay off a little bit.”

The idea of an editor at a Rupert Murdoch-owned publication scolding other journalists for nosiness may strike some as a bit rich. After all, London newspapers pioneered the celebri-fication of the House of Windsor, famously hounding the previous Princess of Wales, Diana, and exposing the most microscopic details of her and her children’s private lives.

In the case of Catherine’s recent whereabouts, however, the British press largely showed an unusual level of restraint.

Yes, they reported on the frenzy of rumors, but mostly in the guise of scolding social media users for spreading conspiracies. When the American outlet TMZ obtained a paparazzi photo of Catherine and her mother in a car, the London papers unanimously declined to publish it.

And once Catherine’s cancer was revealed, British media were quick to assail their counterparts across the pond, accusing American tabloids and media figures of recklessly amplifying the more outlandish rumors. (British libel laws, it’s worth noting, are far stricter than those in the United States.) Piers Morgan, a former tabloid editor himself, demanded that Stephen Colbert apologize for joking about rumors that Prince William was having an affair.

London’s feisty tabloids often claim the moral high ground, but there are other factors at play. The royal family and Fleet Street are a pair of British institutions whose fates and fortunes have long been entwined — and they are facing similar challenges in the new media age.

Gatekeepers who once controlled the official flow of information — be it palace press secretaries or tabloid editors — are increasingly powerless against the online tide. When it was first revealed that Catherine had undergone abdominal surgery, Kensington Palace declared that it would not offer further updates about her condition. Britain’s royal correspondents, who have a long-term relationship with the future king and queen to worry about, mostly abided by that directive.

But both camps were flummoxed by the rampant misinformation that spread on the internet. The tabloids that once led the way in royal sensationalism — and are still grappling with a long-running phone hacking scandal — were now helpless to shut it down. And palace officials, reluctant to compromise the princess’s privacy, mistakenly believed the rumors would fizzle out.

The result was a narrative driven by online chatter that spun out of the traditional gatekeepers’ control.

“I’ve never seen anything like the reaction we had online and the huge conspiracy around this particular story,” Max Foster, a lead London anchor for CNN, said in an interview. “There was a point, about a week ago, where really sensible, bright friends were coming to me and saying, ‘I think there is something going on here.’”

He spent hours discussing with CNN executives how to responsibly cover the rumors about Catherine without spreading misinformation, a balancing act that he called “a real challenge.”

Helen Lewis, a Briton who writes for The Atlantic, also lamented that some of her friends “became Kate Middleton truthers.” In an essay on Friday, “I Hope You All Feel Terrible Now,” Ms. Lewis argued that the situation revealed the frightening power of social media to hijack rational discourse and, in her mind, force a cancer-stricken woman to reveal a private diagnosis.

“If you ever wanted proof that the ‘mainstream media’ are less powerful than ever before,” she wrote, “this video of Kate Middleton sitting on a bench is it.’”

Even British papers acknowledged, however, that Kensington Palace officials deserved some of the blame for allowing an information vacuum to develop.

It was the lack of an official explanation for Catherine’s absence that prompted self-appointed online sleuths to concoct wild explanations. The theory of a cover-up was supercharged after the palace released a doctored photograph of Catherine and her children.

The royals must “come clean about what’s really going on, or risk drowning in a quagmire of their own creation,” Sarah Vine, the Daily Mail’s influential columnist, wrote after the photo fiasco.

Still, the entire episode suggested something that may be reassuring to British royalists. “What this has revealed, in a weird way, is just how relevant that family still is,” said Eva Wolchover, the British American co-host of the royals podcast “Windsors & Losers.”

“For awhile now, the story had been ‘Meghan and Harry are gone,’ ‘We have an older king on the throne,’ ‘Young people don’t care about the royal family,’” Ms. Wolchover said in an interview. “The fact the whole world started talking about this in the past few weeks shows they are still as culturally interesting to us as they ever were.”