The 'Troublemaker' singer was filming a segment with JLS for Channel 4's upcoming charity fundraiser Stand Up To Cancer yesterday (October 9) at SportHouse in Dagenham.
Merrygold 'volunteered' to be shot out of a cannon, choosing Murs to press the 'fire' button.
With hundreds of young fans looking on, Murs pushed the button. However, after nothing happened, he pressed it a second time.
What appeared to be Merrygold then flew out of the cannon and overshot the crash mat, crashing on a wooden stage.
Horrified, Murs looked on as 'Aston' lay motionless with paramedics at his side.
Believing he had caused serious injury to his friend, Murs was soon relieved to discover he was actually a stuntman, and was greeted by the singer, much to the hilarity of the band's other members.
Murs later tweeted: "Still recovering, still shaking & still shocked!! @JLSOfficial you got me proper today!!"
JLS's Marvin Humes wrote: "Just did an amazing prank with @ollyofficial and lots of JLSters!! Absolutely hilarious! Can't wait for u all to see!!"
Davina McCall, Alan Carr and Dr Christian Jessen will host Channel 4's Stand Up To Cancer event on Friday, October 19 at 7.30pm on Channel 4.
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