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The 61-year-old has been taking a break after his bike crash last year, but on this week's episode of AGT, he re-joined judges Howie Mandel, Heidi Klum and Sofia Vergara.
But Simon, who is usually always dressed in trousers and a shirt, could be seen in white shorts instead.
Take a look for yourself in the clip below:
The other judges were pretty amused with Heidi asking: "Are we missing something here? Did you just come back from holiday, or what?"
And Sofia added: "Is it casual Friday?"
Viewers were equally surprised by Simon's new casual look, with one person writing: "l like the relaxed look wear shorts more often, being yourself is more fun."
While another said: "Well that's a first. Simon Cowell in shorts."
And one added: "Simon Cowell wearing SHORTS IM SCARED."
"That's different of Simon lol," commented a fourth.
Simon suffered a terrifying accident last year, when he fell from his electric bike at his Malibu home.
He fell backwards onto concrete and was rushed to Providence Saint John's hospital in Santa Monica.
He took an extended break from the show after breaking three vertebrae and missing his spinal cord by just a centimetre.
Simon later spoke about the incident, explaining: "Some good advice...If you buy an electric trail bike, read the manual before you ride it for the first time.
"I have broken part of my back. Thank you to everyone for your kind messages.
"And a massive thank you to all the nurses and doctors. Some of the nicest people I have ever met. Stay safe everyone."
Simon is literally all of us returning to work in more comfortable attire! We're so glad he's back safe and sound.
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