The music mogul hadn’t even stepped foot inside the venue when he suffered an embarrassing wardrobe malfunction.
Simon was getting out of his Rolls Royce to pose for photographers round the back of the London Palladium when he realised his flies were undone.
The head judge turned around to quickly do them up before telling the press to “shut up” as they laughed at the unfortunate moment.
Friday’s auditions saw presenters Ant and Decreunite professionally for the first time in 10 months.
Ant McPartlin took time out of the spotlight to focus on his recovery after he was arrested and subsequently charged with drink-driving last March.
Asked if he was looking forward to seeing the pair back together again, Simon told reporters: “Of course, I’ve missed them, but now I can rib him. You have no idea what’s coming.”
Ant said he was feeling “really emotional” as Dec Donnelly introduced him on stage.
He told the audience: “I’ve missed you all. As for you [Dec], I’ve missed you. Thank you very much, what a warm welcome.
“What a great show to come back to, I’m thrilled, I’m over the moon. Shall we move on before I cry?”
‘Britain’s Got Talent’ returns to ITV in the spring.