The Chase's Mark Labbett spotted a secret quizzer in the line up of contestants on the ITV show.
Mark, also known as 'The Beast' was tipped off when Kathryn, 28, a learning support officer at a college in Wales, racked up £9,000 in the cash builder - surprising her teammates and fans at home.
When confronting the chaser at the table, Kathryn was offered a low offer of £3,000 and a high offer of £50,000.
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She was advised to go for the £9,000 by her fellow guest even though they thought she could get back with the £50,000 high offer.
Taking on Mark, 55, she easily made it back with her original £9,000 leading Mark to suspect she was a quizzer.
He said: "I knew she was a quizzer."
Kathryn revealed she was indeed a keen quizzer, attending local competitions at a pub and rugby club every Sunday and Thursday.
All four contestants made it to the final chase to play for £16,000 after Lucy took the minus £2,000 offer.
They scored 20 and Mark struggled to chase them down with a number of pushbacks meaning they all went home with £4,000 each.
Kathryn said she is going to use her money to visit her friend in Canada.
Mark added: "The team played well, they did good."
*The Chase is on ITV1 weekdays from 5pm and available on ITV Player
