Brent Eccles was sitting down to dinner several days after he announced the You Are Us/Aroha Nui concerts when he received a text from Lorde telling him she wanted to join the lineup.
"She said, 'Hey, I can't do Auckland but I can come back and do Christchurch'," Eccles recalls.
"I was like really? Really?! Okay - yeah!"
Together with Live Nation's Mark Kneebone, the Eccles Entertainment promoter has been flat-tack working to pull the two shows together.
Tonight's show is taking place at Auckland's Spark Arena, from 6pm.
A second event, with a slightly different lineup, is happening in Christchurch on Wednesday evening.
Both shows boast stellar lineups. Fans at the Auckland show will enjoy performances from Anika Moa, Bic Runga, Dave Dobbyn, Marlon Williams and Six60.
Singer-songwriter royalty Lorde will be gracing the stage at Christchurch Stadium, along with rock band Shihad. They will be joined by a chunk of the Auckland lineup.
Eccles told the Weekend Herald inspiration largely came from the artists. Many had approached him directly, asking what they could do to help.
He approached Kneebone to talk about collaboration, and it was all go.
Eccles said the collaboration was "lovely, but it may never happen again".
"I'm kind of joking ... I mean, we are competitors but with something like this, you put all of that aside."
Proceeds will go to Lianne Dalziel's Our People, Our City fund, established to help raise money to support the families and Muslim communities impacted by the Christchurch shooting.
"There are a lot of mental issues that come up too - people scared to go out, people scared about what happened," Eccles said.
"It requires an army of people to be able to deal with those issues … not just for the next few weeks but for the next few years."
"We're thrilled to be able to give them a big cheque at the end of it."
While tonight's concert is sold out, tickets for the Christchurch show are still available.
Those wanting to catch a glimpse of the Christchurch event on the small screen will be also able to tune in on TV3 - where it will be broadcast live.
International security experts are being brought in for the Christchurch show, and Auckland's Spark Arena will also have a high level of security.
Both shows would open with collaborative performances, Eccles said.
He also expected some impromptu collaboration between acts throughout the night.
"A band like Shihad will be playing Shihad songs, same with a band like Six60."
"But you never know who's going to jump up and join - that could happen too as the night goes on."