Those JLS lads love nothing more than a prank - remember the Ortise Williams' birthday surprise or Marvin Humes' getting strapped to a dwarf on his stag do?
The Xtra Factor presenter was left shaken after he believed a human cannonball stunt had gone wrong, and left 'Aston' dead.
Olly believed he was live on Channel 4 presenting and had to hit a button so that Aston would shoot out of a human cannon to launch Stand Up To Cancer.
'Aston' overshot the padded area and into a large wooden stage, which left Olly frozen while the JLS boys dashed over to see if their bandmate was ok.
After two, long minutes, Aston reappeared, revealing a stuntman had taken his place, much to Olly’s relief.
After the event, Olly was still getting over the prank, tweeting: "Still recovering, still shaking & still shocked!! @JLSOfficial you got me proper today!!"
Marvin added: "Just did an amazing prank with @ollyofficial and lots of JLSters!! Absolutely hilarious! Can't wait for u all to see!!"
The prank airs as part of Stand Up To Cancer on Channel 4 on Friday 19 October.