From Rolling Stone:
"Lady Gaga will join Metallica onstage at the Grammys this Sunday. On Monday, a Gaga fan site tweeted a snippet of a Grammy promo clip declaring, "Lady Gaga duets with Metallica." Rolling Stone has confirmed the collaboration.
This is the latest move in an impressive week from Gaga. Following her well-received Super Bowl halftime show on Sunday, she announced that she will tour arenas and stadiums all over the world behind her album Joanne, which came out last October. Billboard predicts that Joanne will jump back into the Top 5 on the Billboard 200 next week as listeners scoop up copies following her Super Bowl performance."