As the final three acts were left on the stage, he said: "Okay, there you go then, we are left with Tokio, Daliso and Jess. The public chose you…
"Sorry! Issy! Issy! And Issy! Ooh, she's going to out a spell on me now."
After he made the blunder, the young magician could be seen turning to the presenter in shock and asking: "What?!"
As Ant noted that he had made an error both the judges and the audience could be heard chuckling at the youngster's reaction.
Britain's Got Talent: Ant accidentally called Issy by the wrong name
Britain's Got Talent: Issy Simpson was not impressed by Ant's blunder
The 41-year-old then apologised for his mistake, laughing: "Alright, I made a mistake, don't rub it in."
Issy sadly did not win the competition but she appeared to be thrilled for Tokio Myers who was crowned this year's champion.
The pianist collapsed after Ant and Dec announced that he was the winner of this year's series.
Britain's Got Talent: Issy could be seen scolding Ant in the final Britain's Got Talent: Most memorable moments Mon, May 1, 2017
Britain's Got Talent: The best and worst moments from the ITV talent show.
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Dance act Just Us get the golden buzzer
Britain's Got Talent: Tokio Myers collapsed on the stage when he was crowned the winner
Shocked, the 32-year-old commented: "I can’t believe what has just happened!”
But the judges agreed that he was a worthy winner with Simon Cowell telling him: "This was the most important thing. I’m thrilled for him."
David Walliams added: "It’s fantastic. He is going to be a fantastic ambassador for the show. He oozes talent."