The presenters were walking into Gwrych Castle to start Friday's instalment of the ITV show when Dec suffered the wardrobe malfunction.
"Hello, good evening! Oh I just popped open my buttons!" he shouted, patting at his chest in a panic.
Ant was so wrong-footed by the situation that he stumbled and whacked into a candle with his arm.
— I'm A Celebrity... (@imacelebrity) December 3, 2021
"Oh no, I knocked a candle off!" he exclaimed, as crew members could be heard laughing.
Dec then asked if they could just start over, even though they were live.
"We are not live are we?" Ant quipped. "Are we live?"
The TV stars then jogged back to the entrance and stepped outside the door to start again, with Ant urging viewers: "Pretend it didn't happen."
"Take two," Dec announced, before the pair came back through the door and started again.
Viewers thought the incident was absolutely hilarious and praised the presenters for handling the live TV snafu so well.
One person posted a message on Twitter saying that Ant and Dec had made her day.
"What a great entrance - Dec pops a button and Ant nearly caught fire," tweeted another.
One posted: "Dec buttons popping off. Take two. The show hasn’t even started yet and I’m already in bits laughing."
"The chaos of Ant and Dec just cracks me up," another fan wrote.
One said the pair were "just brilliant, even when it all goes wrong".
"Just spat my drink out at Dec's buttons on his shirt popping open in the first 2 seconds," said another amused viewer.
I’m A Celebrity…Get Me Out Of Here! is on ITV and ITV Hub.
Watch: Piers Morgan desperate to end Ant and Dec's NTAs streak