During Mastodon‘s set at the Portugal’s Rock in Lisboa Festival last month, there was one crowd member who stuck out from the rest.

Fully geared up with Metallica merch and a Halloween mask over his face, the crowd member attended the rocking musical evening while swaying to Mastodon’s beat.

However, due to closer inspection from fans, the masked fan was reportedly none other than Metallica frontman James Hetfield.

Set to play the festival later into the night, the masked Hetfield was checking out Mastodon’s May 25 set while being closely watched by security. An eyewitness account as well as a picture of the masked man was posted on 9gag, where the story was told in full:

So, during Mastodon at Rock in Rio, into the snake pit comes a guy fully dressed in metallica apparel, hoddie over the head, gloves in hands (with that heat!) and a mask. I was “ok, seen weirder stuff” and continue to rock on. But a friend of mine (the blonde girl on the picture below) grabbed me and said: ” That’s James!” And it really was him. Made some eye contact with him a few times, it really were his blue eyes. Also, the way he was rocking out, full of his manerisms (is this how you spell it?).

To add everything up, there was a security guy (not from the venue’s security) at the entrance of the pit, ALWAYS looking at him. To top it off, Jeff came in and snapped a few pictures of him. James was right behind me.

Most of the people in the pit didn’t notice it, but the ones around him did. Nobody made a fuss about it, we let the man rock out, but we KNEW, and he knew we we’re on to him. In fact, he elbowed this friend of mine twice in a row, despite the fact she was not too close to him. Elbowed her once, she didn’t care, elbowed her twice, she looks back and he’s all relaxed, just watching the show… ;) He wanted us to notice him.

A few songs later, he walks out and a venue security grabs him; the other security guy that came with him talked with him. We couldn’t hear of course, but we later went to the venue security and asked him “Hey, was that James?” and his reply? “Yeah, he was in Metallica.”.

Very sneaky, Hetfield. It’s pretty cool to know that the Metallica frontman is still in tune with modern metal, having braved the massive crowd at the Portuguese fest to check out Mastodon. If someone had ripped Hetfield’s mask off, the crowd would have likely converged zombie apocalypse style and could have even broken Hetfield’s legs … all four of them. Zing!