Early on Wednesday, a BBC journalist sent out a tweet that briefly created chaos in newsrooms around the world: "Queen Elizabrth [sic] has died."

“BREAKING: Queen Elizabeth is being treated at King Edward 7th Hospital in London,” BBC reporter Ahmen Khawaja followed up in a second tweet. “Statement due shortly.”

The queen, however, had not passed away. Also, while it turned out Queen Elizabeth II was in the hospital for an annual checkup, this appeared to be a coincidence.

Khawaja claimed her tweets were sent in error, and she soon deleted them. The BBC issued a statement that suggested the tweets had been sent during a “technical rehearsal for an obituary.”

The tweet did not reveal the death of a monarch, but it did offer a glimpse of the BBC's remarkable preparation for its coverage of the death of a sitting monarch.

Any news that the British monarch, currently 89 years old, could have died or was likely to die soon, would be momentous. For one thing, Queen Elizabeth is a popular figure; it's not too much of an exaggeration to say that she is holding the royal institution together (the next in line to throne, Prince Charles, is not so popular).

The BBC is Britain's public service broadcaster, and it approaches the reporting on the deaths of royals with a somber professionalism. It currently lists four royals -- the queen, the Duke of Edinburgh, Prince Charles and Prince William – as "Category 1" on a list that denotes how much weight to give the news of the death.

Since 2010, these royals have been the only members of "Category 1." Lower ranking royals such as Prince Harry are listed as "Other Notables," according to the Daily Mail, given the same importance as public figures, such as President Obama or Mohammed Ali.

If a member of "Category 1" dies, it is a huge event, as it has been in the past. Normal broadcasting is interrupted for an official announcement, likely a statement from Buckingham Palace, the administrative center of the monarchy. The national anthem is played. And, as it was after the death of King George in 1952, all comedy on the BBC network is expected to be cancelled until the funeral is held.

BBC journalists, such as Khawaja, are expected to rehearse for such an event. In his book “On Royalty,” BBC veteran Jeremy Paxman describes how in the '70s and '80s, journalists would come in on a weekend day every six months to practice what would happen when the mother of Queen Elizabeth II died.

“Long sets of guidelines were produced and laminated in plastic. Elaborate chains of editorial command were established in which people identified only by impenetrable acronyms would refer the news up,” Paxman wrote. “Reporters would be dispatched to empty corridors and car-park basements, pretending to be at the gates of Buckingham Palace, St James’s Palace or Clarence House.”

Another BBC journalist, Peter Sissons, also wrote in his memoirs about rehearsing for the death of the late Queen Mother.

"Every six months or so, we rehearsed all this. A news ­studio was set aside on a Saturday morning and we worked through a fictional scenario," Sissons wrote. "We usually pretended that she’d expired after choking on a fish bone — something for which she had form — at her Caithness home, the Castle of Mey. The remoteness of the location posed particular ­technical challenges which our rehearsal was expected to help identify."

Sissons even had to have a specially-made suit, appropriately somber, on for the sad event – though in the end it was his decision to wear a red tie on the day that resulted in a number of complaints. Clearly, the pressure on BBC journalists on such a day is immense: "Please God. Don't let it happen on my shift," is how the Tim Luckhurst, a former BBC editor, put it in 2001.

The Queen Mother passed away in 2002, and plenty of things have changed in the world since then. However, the basic BBC procedures may not be quite so different. According to Tom Sykes, the well-connected royal correspondent for the Daily Beast, the BBC will still make an official announcement about the death on air, not on social media.

Which brings up the most perplexing part of Wednesday's accident: It happened on Twitter. Journalists had been told specifically not to use social media during the rehearsal, the Telegraph reports, and some now suspect that Khawaja, who reportedly was not part of the exercise, must have overheard the rehearsal and mistaken it for the real thing. The BBC is now said to be conducting an internal investigation.

For her part, the BBC reporter later tweeted that she had left her phone at home, and it had been a "silly prank." That tweet, in turn, has since been deleted.

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