It's not every day you see Celine Dion hanging out with Jack Black at a Metallica concert ... but that's exactly what everyone saw Saturday night in Las Vegas!

As you can see in this video, the pop star, known for her soaring ballads, loves head-banging music and is seen rocking out with Jack to one of Metallica's classic tunes, "Enter Sandman."

At one point during the song, you see Celine playing air guitar and showing off her own headbanging skills. Meanwhile, Jack is totally digging the band as well, leaning back and mouthing the words to the song.

The two stars are then seen side by side clapping their hands over their heads during a guitar solo. Jack wraps it all up by once again belting the lyrics while boogieing down.

Metallica kicked off their "Life Burns Faster" residency at the Sphere on October 1. The group -- consisting of frontman James Hetfield, lead guitarist Kirk Hammett, bass guitarist Robert Trujillo, and drummer Lars Ulrich -- is slated to perform 24 shows at the Vegas venue through March 13, 2027.

And this isn't the first time Celine caught the band live. She rocked out to Metallica just a few days ago -- and there's video of her wildly playing air guitar.