The Former Today host dressed up as a clown as part of an unusual segment on Monday's episode of This Time Next Year.
After guest Scott Cunningham pledged to overcome his phobia of clowns, Karl threw on a red nose, colourful wig and rode a mini bicycle to test him.
WATCH: Karl Stefanovic pulls bizarre stunt as he dresses like a clown to help man overcome phobia
Scott told Karl that his "embarrassing" phobia stemmed from watching the Stephen King thriller It as a young child.
"It's not just scared, but it's even more than that," the father-of-two confessed.
"I actually have a different type of fear where I don't run away, I actually get quite violent and attack the clown."
In addition, Scott revealed that when he sees a clown, he gets "anxiety straight away, my heart pounds and I get short of breath."
Scott appeared to be holding back tears as he explained that his This Time Next Year goal was to be able to take his children to the circus.
After a year of therapy treatment with psychologist John Malouff, he returned to the show to reveal whether he had achieved his goal.
Karl Stefanovic dressed up as a clown as part of an unusual segment on Monday's episode of This Time Next Year.
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"I've completely overcome my fear of clowns," Scott announced, adding that he had taken his children to the circus (and even got a tattoo of a clown on his leg).
To make sure the proof was in the pudding, Karl threw on his clown outfit and rode around on a bike onstage to test Scott.
"Any anxiety?" the 45-year-old asked.
"None whatsoever, you just look a bit silly," Scott said with a laugh.
This Time Next Year airs Mondays at 8:45 pm on Channel 9.