She blamed her confusion on the time difference between the UK and her current location, Bhutan, which is six hours ahead.
But her mea culpa didn't stop Bake Off fans venting their fury via an explosion of memes on social media - many of which predictably featured Prue's revered predecessor, national treasure Mary Berry.
Leith, a trained chef and restaurateur, was quick to delete her explosive tweet, but not before inadvertently spoiling the result for thousands of viewers of the Channel 4 show.
The tweet posted by Prue at 10.37am read: "No one told me judging a GBBO final would be so emotional. I wanted them all to win. Bravo [name redacted]."
Leith expressed regret for her blunder, initially saying she was in "too much of a state to talk about it".
It was before 5pm in Bhutan when she tweeted the name of the winner, but given that the country is six hours ahead of the UK, it doesn't explain why the judge thought she was safe to let the cat out of the bag.
When she first broke her silence following the slip-up, an upset-sounding Leith said: "I'm in Bhutan. The time difference is massive. I thought that they got it six hours ago. I'm in too much of a state to talk about it. I f***** up."
Presenters Noel Fielding and Sandi Toksvig are yet to comment on the incident.
Leith's gaffe sent Bake Off fans into a frenzy, with many responding by sharing comical memes inspired by the judge's astronomically ill-advised tweet.
Many gags featured Mary Berry, who was Paul Hollywood's fellow judge on the much-loved show when it was on the BBC.
When she stepped down following the announcement that the show was moving to a new home on Channel 4, Prue was selected as her replacement - and fans were quick to joke that Berry, 82, might derive some satisfaction from the slip up.
