The onstage collaboration was far from perfect, with Metallica frontman James Hetfield suffering sound issues onstage during the performance of Moth Into Flame, but bandmates Kirk Hammett, Robert Trujillo, and Lars Ulrich were more than impressed with Gaga.

Prior to the performance, guitarist Hammett said, "When it was suggested that Lady GaGa do it (with us), we thought, 'That's interesting', but when she came down to actually work with us with the song, it turned out really, really, really well. I mean, she was really open and willing to work with different arrangements and see what worked well over the course of the song.

"It was great. She was really, really great to work with."

And bassist Trujillo added, "She's got a lot of edge and attitude, which is important for what we do. And she actually came to see us play... We did a small show at the Henry Fonda Theater (in Los Angeles), and she saw the whole show... She was rocking out."

And now Metallica drummer Ulrich has offered her a permanent spot in the band, inviting the Poker Face singer to join the band onstage whenever her schedule allows.

"We've got a new lead singer," he told Access Hollywood. "Well, a new co-lead singer, is a better way of saying it. We were talking earlier about maybe making her a permanent member of Metallica, and being a five-piece from now on, so we'll see."

The drummer admits he's been a fan of Gaga's for some time, and he was very impressed by her Super Bowl spectacular earlier this month (05Feb17).

"She killed it," he added. "I mean, it was unbelievable. I think that at a time right now where everything in this country is so divisive, the one thing that everybody could agree on last week was that she just nailed it better than anybody ever, so it was awesome."