AC/DC didn't tell their sound engineer Brian Johnson, Cliff Williams and Phil Rudd were returning for their new album.

The legendary rock group - also comprising of guitarists Angus and Stevie Young - are back with their first new music since 2014's 'Rock or Bust' album on Wednesday (07.10.20), when the single 'Shot In The Dark' will be released.

And Mike Fraser, the group's long-time engineer, has revealed they kept the news of the singer, bassist and drummer's return so under wraps, he didn't find out until they all arrived at Vancouver’s Warehouse studio to start work on the record, which appears to be called 'PWR UP'.

Fraser told the AC/DCFans.Net podcast: "As far as I knew, Brian had retired, Cliff had retired, and with Phil and some of his problems he's had in his home country [of New Zealand], who knew if he was even gonna be allowed out of his country.

“Walking into the studio … the first day, I had no idea what was gonna happen. When I got there, none of the band had arrived yet, but a lot of their techs were there … and one of the guys said, ‘Hey, you know what's going on?’ And I said, ‘I have no idea. I just know we're here and we're setting up.’ And he goes, he says, ‘Well, the whole band’s here: Brian, Cliff, Phil and Stevie, and they’re here and we’re ready to rock another record.’ So, man, it was such a shocking, awesome surprise.”

Johnson is returning to vocals following a four-year break, after he was forced to quit the group in 2016 on doctor's orders due to progressive hearing loss.

Sticksman Rudd, meanwhile, was replaced on the 'Rock or Bust' tour in 2015, after pleading guilty to a threat to kill charge and for possession of methamphetamine and cannabis.

Bassist Williams had also retired in 2016.

Fraser also revealed that Brian and late band member Malcolm Young had "written tons of songs” with Angus before he passed away in 2017, and so some of his riff ideas will be on the new LP.

He added: “Angus kinda came into this with a lot of ideas and riffs and not too many completed songs.

”But that was similar on 'Rock Or Bust'. Because him and Malcolm [Young] had written tons of songs before Mal got sick and eventually passed away. So he's got a whole treasure trove of ideas and riffs and all that. So he's probably spent a few years before we came in to do this record pooling ideas together and all that, and then when he came into the studio here, he just sat down with a whole suitcase full of little demo things he had done. And him and Brendan O'Brien, who produced the record, would sift through all the ideas and say, ‘Hey, that's great. That's a really good song. Let's put that riff here.'

“He had — I don’t remember exactly — maybe three or four songs sort of completed that they maybe adjusted, added a chorus here or something like that. But yeah, it was just basically from a stockpile of all these riffs and stuff that Angus and Mal had put together over the years. So they had to sort piece the songs together before we'd record them. They'd probably spend a day or so doing that, and we'd come in, blast off the song. And like these guys work, it's pretty much live in the studio. What you hear is what they did, what you get. They fire up pretty quick. They all work really good together, 'cause they've worked together for so long; they're a unit.”