According to Instagram posts shared by the band, Metallica fan Joice M Figueiró was 39 weeks pregnant when she attended the show at the Estádio Couto Pereira, and began going into labour as the band started to play Enter Sandman.
James Hetfield has since contacted the mother and her husband to send them his well wishes.
Although the full phone call wasn't recorded - the conversation actually lasted seven minutes - the proud parents shared a few seconds of it onto their Instagram stories.
“This is James from Metallica, congratulations, you guys,” Hetfield says.
“Oh my God. Hi,” Joice responds. “I cry.”
During the gig, medics arrived on the scene and attempted to take Joice to a local hospital by ambulance. However, the baby had to be delivered at the venue towards the latter end of Metallica's performance.
The baby was born safely, in Joice's own words, "to the sound of Enter Sandman". Her son Luan "came to the world on 07/05/2022 at 23:15, shaking all the metal structures", apparently.
"Every show I go to, something has to happen, but this time I think I've outdone myself," Joice joked, later acknowledging in two Instagram stories that her experience had gone viral and adding that she was "great physically and trying to understand how this happened."
"He was born right there, in Couto Pereira, to the sound of Metallica," she noted via a story. "Everyone was surprised at what is happening."
In a new interview with The Washington Post (opens in new tab) Joice elaborated on the experience, explaining: “It was a mix of emotions. Since it wasn’t planned, I was scared that the medical team wouldn’t be ready. But there’s also the feeling of being able to tell people that this happened because Metallica is one of the bands we love the most.
Following the event, Joice thought it would be fitting to name her baby something Metallica-related. “I joked that [Luan’s] name would be James Ulrich,” she said.
“But really, since this name question has brought up great appeal and we haven’t registered him, we’re thinking of maybe adding a [middle] name and putting some homage in there.”
One name that she did not approve of though was "Sandman".
“Remember, this is the name he’ll carry throughout his whole life,” she explains. “He’ll get bullied with the name ‘Sandman.’ He already has enough of a story to tell.”
Check out the clip of the Hetfield call below: