Watch Foo Fighters bring out Gene Simmons at Las Vegas show

The great thing about going to a Foo Fighters concert is you never really know what kind of surprise awaits. For fans in Las Vegas, that meant catching a glimpse of Gene Simmons.

After spotting a fan who looked a lot like the KISS bassist, Dave Grohl convinced Simmons to come out from side stage. Wearing a face mask, he didn't do much other than hand Grohl what appeared to be a receipt before walking backstage again, but that was enough for the crowd to erupt in applause.

“Can we just hear it one more time for Gene f***king Simmons,” Grohl exclaimed.

"I had posters of that mother f***ker on my wall when I was a kid. Let me rephrase that," he said, adding after a short pause: "I still have posters of Gene Simmons on my wall at home."

In the comments, a user called unknownamus revealed that he was the fake Simmons in the crowd. “Hey, this is the fake Gene Simmons saying thanks to everyone who tried to get me on stage!" he wrote. "Too bad security turned me down. I legit through when Dave said ‘Gene, get up here!’ he was talking to me, but he meant the REAL DEAL! Fair trade in my book.”

Watch it all go down above.