The 53-year-old rocker's vocals were completely inaudible in Los Angeles' Staples Center on Sunday (12.02.17) during the group's duet with Lady Gaga because his microphone was switched off, and though he overcome the difficulty by sharing the 'Poker Face' hitmaker's mic for the second part of the performance of 'Moth Into Flame', his bandmates had never seen him so angry for years afterwards.
Drummer Lars Ulrich said: ''I haven't seen him like that in 20 years.
''I mean he was livid. I mean, he's aged really well and he's a pretty chill guy, but the first five or 10 minutes in that dressing room was not a lot of fun.''
But despite the mishap, the group powered through as best as they could as they didn't realise the extent of the difficulties and think they were still able to produce a solid performance.
Speaking to 'Late Late Show' host James Corden - who also presented the Grammys - Lars said: ''Well, in the heat of the battle you're out there you're playing when it's a technical issue you don't really know is it going to the house, is his vocals gong to the truck? Maybe it's the monitors, so you just gotta keep playing.
''We fought through it, and, you know, with the fire and Gaga in my lap for a minute at one point, it was just keep going, keep going, keep going. So we just fought through it, and a lot of people said it at least made for great television.''
And this wasn't the first time the 'Nothing Else Matters' group - which also includes Kirk Hammett and Robert Trujillo - have had an embarrassing moment on stage, as one concert saw Lars spend 15 minutes off the stage, although he was still bashing away on the percussion instrument.
He explained: ''In 35 years we've had a few mishaps.
''I spent 15 minutes playing two or three songs under the stage.''
Once a fire fighter, always a fire fighter.
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