Ahmen Khawaja, a reporter for BBC Urdu, sent out a tweet saying: "Queen Elizabrth [sic] has died."
Another tweet from the account of Khawaja said: "BREAKING: Queen Elizabeth is being treated at King Edward 7th Hospital in London. Statement due shortly: @BBCWorld."
The incident happened during one of the corporation's regular rehearsals for broadcasting the British monarch's obituary, which BBC bosses had asked staff to keep off social media.
Khawaja later deleted the original tweet and called it a false alarm.
"False alarm to Queen's death! She is being treated at King Edward 7th Hospital," she tweeted.
A BBC spokesperson said: "During a technical rehearsal for an obituary, tweets were mistakenly sent from the account of a BBC journalist saying that a member of the royal family had been taken ill.
"The tweets were swiftly deleted and we apologise for any offence," the spokesperson said.
Buckingham Palace, too, was forced to take the unusual step of issuing a statement reassuring the British public that their 89-year-old Queen was in good health.
Coincidentally, the Queen attended a London hospital for a "routine" annual check-up.
"I can confirm that the Queen this morning attended her annual medical check-up at the King Edward VII's Hospital in London. This was a routine, pre-scheduled appointment, the Queen has now left hospital," a Buckingham Palace spokesperson said.

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