It was all a rehearsal..
The NBC report says this:
The initial report was picked up by media outlets including CNN Newsource and German newspaper Bild.
However, when NBC News alerted Buckingham Palace to the tweets, a spokesman said that the queen was not only alive but carrying out public engagements.
It is not clear exactly how the mistake happened but the U.K.’s publicly-funded broadcaster was staging an internal drill on Wednesday to examine its readiness for the queen’s death, a routine event staged by many news organizations.
The reporter who tweeted the death notice deleted said evidence of the non deaths..