It appeared he thought three of the four judges had opted to send Michael home, meaning she would have been automatically out of the competition.
It was later clarified that two judges wanted to send Michael home, while the other two chose to send Stephans home, meaning it was a deadlock and would go back to a public vote.
Flack then announced: "The act who received the fewest votes from the public and who will be leaving the competition tonight is ... it's Monica Michael."
When the show was over, Murs sent out a tweet acknowledging his blunder.
He also joked about the "massive boo-boo" and alluded to the fact it may get him fired.
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"I think I'm not going to be back next week," he said to his fellow judges.
The incident prompted a reaction from fans, many of whom came to his defence following backlash including allegations the result was rigged.
-AAP