Bradley Walsh was ecstatic after former maths teacher Mark Labbett answered a maths question incorrectly.
On The Chase today was Willie, Sarah, Harry and Christine, all hoping to win a huge amount of money.
Willie set the team up nicely by securing £3000, leaving the second contestant Sarah to add to the prize pot.
After winning £4000 in the cash builder, Sarah started strong in the head-to-head against The Beast.
And it looked like she could easily take back her £3000 after Mark incorrectly answered a maths question.
Bradley asked the pair: "In maths, what is the first composite number."
The options were either two, four or six.
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A composite number is a whole number that can be made by multiplying other whole numbers.
While Sarah got the question correct, former maths teacher Mark Labbett gave the wrong answer of four.
Informing the contestants of Mark's previous employment, Bradley was grinning from ear to ear.
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Brad said: "We have found a chink in the beast's armour - composite numbers."
Mark explained that in his 20 years of teaching, he'd never heard the term composite number.
He told Bradley: "You'll just enjoy the fact I got it wrong."
