The BBC reporter who sent a tweet mistakenly claiming the Queen had died had not been told the corporation was running a rehearsal of how it might cover a royal death.
A report from the BBC Trust’s Editorial Standard’s Committee said the publication of the tweets were a “serious breach of editorial guidelines”.
It said “some news staff” had been emailed about the plan and told not to discuss it, but added: “A journalist working for the BBC’s language services, who had not been sent the email, saw an internal TV monitor which was showing the rehearsal.
“A number of tweets were sent from her Twitter account. The first stated that the Queen was being treated in hospital, the second stated that the Queen had died; the tweets included a link to BBC World’s official Twitter feed.”
Those messages sent by BBC broadcast journalist Ahmen Khawaja were in turn reported by news outlets around the world.
The BBC Trust said the tweets were “a grave error of judgment” and added it “profoundly regretted any distress that had been caused”.
Ms Khawaja is facing disciplinary proceedings over the tweets, which were coincidentally published on the day the Queen was at hospital for her routine annual medical check-up.
Buckingham Palace took the unusual step of confirming the private medical visit after concerns were raised about her well-being following the tweets.