Britain's Got Talent viewers believe The Haunting's trick was 'set up' after hearing Simon Cowell's remark.
Amanda Holden was left in tears and even swore live on air after being terrified by magician Elizabeth and some 'ghosts' for a second time.
The horrified BGT judge then screamed "f***" live on air when 'Agatha' transformed into Elizabeth - but viewers were convinced the magician's trick was .
However, some people noticed a comment that Simon made to Amanda right at the start of the performance.
At the very start of the act, Elizabeth told Simon and Amanda to turn and face each other.
Trembling Amanda, who knew something terrifying was coming, said: "My heart is going already."
But Simon was not in the mood to comfort her and replied: "Stop over acting."
Lots of BGT viewers raised their eyebrows after hearing Simon's comment and took to Twitter to give their take.
One viewer said: "Simon just tell Amanda to ‘stop over acting’.... confirmation it’s all set up"
"So Simon Cowell just told Amanda to stop overacting.... kind of killed the act before it even started," added another.
A third said: "Christ alive, Amanda Holden is a terrible actor. Did have to laugh when Simon told her to "stop overacting" though. Clearly rehearsed. Load of tosh"
Hahahaha Simon telling Amanda ‘stop overacting’, anyone else see that," said a fourth.
This wasn't the only part of the act that caused controversy during Monday night's first live semi-final.
Amanda was led down to a dingy basement and was given the fright of her life when she was grabbed by 'Florence' the ghost.
She started screaming again when another ghost, 'Agatha', broke through a mirror and grabbed her arm.
As they headed up the stairs, BGT viewers claimed they spotted Elizabeth hiding round the corner.
Her head and arm wee seemingly poking out, which made the big twist appear less impressive.
Amanda didn't notice the swap taking place as she shouted "f***" when she turned round and saw Elizabeth behind her.
After spotting the gaffe , one viewer tweeted: "The Haunting...anyone else see the other girl coming out of the stairs to take over from “Agatha”?"
"The haunting wasn't even real, you could see the woman change on the stairs," added another.
A third said: "Did anyone else notice the woman standing on the stairs ready to swap over on the haunting act?"
"The haunting’s camera man after realising he’s getting sacked for exposing the act as fake at the stairs," joked a fourth.
*Britain's Got Talent airs tonight on ITV at 7.30pm with results at 9pm
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