It's "Geronimo," the first internationally reaching single from Australian indie pop act Sheppard, and it's come to take over the world. That's not to say "Geronimo" is all that the six-piece is and ever will be, but it's a heck of a good start. Released in February 2014, the song conquered Australia, then set its sights on the rest of the world, going top 10 in multiple countries, including much of Europe. Next up: America, where the song is already getting spins at KROQ (a CBS Radio station) and just broke into the Billboard Hot 100.

And that's not bad for a song that just sort of happened by accident. According to George Sheppard, frontman and one of three songwriters of the band (as well as one of three Sheppards; his sisters Amy and Emma also populate the group), "Geronimo" started as a spontaneous idea just moments before a gig, courtesy of guitarist Jason Bovino.

"We were literally about two minutes from going on, and Jay had found this little wooden DJ booth at the back of the stage, and he kind of stepped into that," George tells Radio.com. "He was wearing these big, thick boots and started stomping on the wood. It made this big reverberating sound all throughout the backstage. He called Amy and I backstage and he started playing that opening 'Geronimo' riff; I think he had a Mumford & Sons-y type of vibe to it.

"It was like a lightbulb moment; there was something so engaging about that way he was strumming the guitar that we instantly started singing that opening melody, that 'Can you feel it?' I don't know, it was just one of those songs that comes out of nowhere and blindsides you."

Sheppard's story accelerated in 2014, but it started in 2009. George--at the time in acting school--met up with Amy, who he says "wanted to be a musician from an early age." The two collaborated on the harmonies of an unfinished song, and suddenly it all clicked. Later, the band filled out with other members, including younger sister Emma on bass.

But it was no von Trapp children situation, as Sheppard is quick to point out. The sextet's musical attack varies, but it all comes back to the dual-vocal approach with George and Amy, who either trade off lead vocals or harmonize together. Think Of Monsters and Men in a more modern sense, sure, but their main influence goes back a bit further.

"Growing up in Papua New Guinea, we didn't get a lot of access to new music, but we'd listen to a lot of what our parents were listening to--like Eric Clapton, Cat Stevens and Fleetwood Mac," Sheppard says. "Fleetwood Mac is a big one for us, with all the boy-girl harmonies and the style of music they were making. That style of pop music was a huge influence on us. All those old-school pop acts' Even nowadays we have all these different influences and all have different iPods, iPod playlists. I think that is the aspect that sort of makes us who we are."

That approach first found the band success in 2013, when their song "Let Me Down Easy" was a top 20 hit on the ARIA Singles Chart (the Australian music sales charts), scoring a nomination for Best Independent Release at the ARIA Music Awards. A year later, at the 2014 awards, Sheppard was suddenly nominated seven different times, including for Album of the Year for their debut full-length Bombs Away and Song of the Year for "Geronimo." Though they only won once, for Best Group they did beat out the likes of 5 Seconds of Summer.