The blonde judge, 49, is seen with her head in her hands after the head judge, 60, takes part in a dangerous act.
Fans will see stunt man James begin his audition by asking Simon to push down on the plunger of the fifth box of explosives that was in front of the panel.
As soon as he does, there is an explosion, leaving hosts Ant and Dec jumping in surprise.
But this is just the start of the act.
James then asks Simon to pick one of the four boxes that are left, and he chooses the box furthest from the one that has just exploded, with James saying: “His intuition is a test of bravery and some would say pure craziness.
“Simon you’re going to make a series of choices, I believe this is one of your better ones. Please choose a number between one and four.”
After picking box number two, James then asks Simon to come forward to push down the plunger – however viewers will have to wait until tonight to see what happens.
Tonight’s episode will also see David Walliams nearly have his manhood crushed by a motorbike.
The judge lies down and cups his privates as daredevil rider Jack Price reverses to within centimetres.
Afterwards, David, 48, says: “I’ve never had a motorcycle touch my testicles before”, and jokes that the ITV show’s producers “got their money’s worth”.
During the stunt, which also sees David wearing a Union Jack helmet, judge Amanda Holden looks aghast and Alesha Dixon begs: “Please don’t hurt our David.”
But Simon quips: “It was so exciting seeing David nearly get hurt.”
David adds: “It was scary because I’d never seen that guy before.”
“I mean, I’m assuming he’s good at what he does.”
“All I could do was remain still, stare at the ceiling and put my trust in the show that I wasn’t going to get hurt.”
“I couldn’t really see what was going on.”
- Catch all the action on TONIGHT at 8pm on ITV.