Leith accidentally announced the winner in a tweet hours before the finale aired on Tuesday.
The tweet was hastily deleted and Leith tweeted an apology for the spoiler, explaining she was in a different time zone when she sent it out.
"I am so sorry to the fans of the show for my mistake this morning," her tweet read. "I am in a different time zone and mortified by my error #GBBO."
But the incident had already left a bad taste in some viewers' mouths, especially coming on the heels of the furor over judge Mary Berry leaving and being replaced by Leith.
The amateur baking competition is a cultural phenomenon both in the UK and abroad.
Last year it was announced that the series was leaving the BBC for a new home on Channel 4.
Soon after, hosts Sue Perkins and Mel Giedroyc and judge Berry announced they would be departing the show.
The gaffe by Leith apparently didn't stop viewers from tuning in, however.
According to The Guardian,"The programme attracted an overnight audience of 7.7 million, a 34.6% share of the audience and well above the average for the series before the final of 6 million."
For those who missed Leith's tweet and were wondering, contestant Sophie Faldo won.
Copyright 2024 by Cable News Network, Inc., a Time Warner Company. All rights reserved.