The latest viral hit: Gotye

As I write this, the YouTube view count is at 45,405,285. By the time you check out Gotye's Somebody That I Used to Know video, another million may have been added to that giddy figure.

It's an intimate, intense, lo-fi song about the end of an affair. And a breath of fresh air in comparison with the high-gloss, budget-busting productions of so many MTV favourites.

Gotye's not afraid to bare (almost) all on it, either. Mostly in close-up, the Melbourne musician's face and naked body is slowly painted with geometric shapes in pastel shades until he blends into the wall pattern behind him.

Meanwhile, he sings quietly about a finished relationship, growing more passionate as the chorus arrives: "I don't even need your love, but you treat me like a stranger and that feels so rough." At two-and-a-half minutes comes the twist, a verse from the woman's perspective sung by cute Kiwi up-and-comer Kimbra Johnson.

She also appears naked with her back turned, slowly losing her own paint as a symbol of the pair's separation (though in real life Gotye is in a steady relationship with another musician). They sing in each other's faces with such emotion that it evokes the awkwardness of witnessing a real-life public bust-up.

The song itself has an unusual quality for a pop smash - it's a grower. Starting with a simple bass and acoustic guitar sample, it then features a xylophone part which has been compared to Baa Baa Black Sheep. It's the slow-building angst of the vocal, followed by the arrival of the woman's voice as it suddenly becomes a duet, that makes it memorable. "I spent six months considering giving the song away, it was so frustrating trying to find the right vocalist for that part," says Gotye. "When Kimbra finally stepped in I felt right away that she was going to have the special darkness that would make it work."

The single may only be at No 36 in this week's UK chart but it is already a gigantic hit. For YouTube comparisons, the current No 1, Jessie J's Domino, has been seen 16 million times, while Lady Gaga's most recent epic production, Marry the Night, has 30 million hits. Far more people want to watch this skinny unknown with his top off.

It was first released in Australia last July, where it became the longest running No 1 by a homegrown artist since 1997. Now, the biggest problem is reaching other countries quickly enough - the internet is much faster than his tour schedule. Just before Christmas the track had to be rushed out in Germany because radio stations there had put it on their playlists before they had even been given it by his record label. It went to No 1, as it has in Austria, the Netherlands, Belgium and New Zealand. "Its success constantly surprises me," says Gotye.

In Canada an unknown indie band called Walk Off the Earth have started selling their cover of the song first. A video of the quintet performing it while all playing the same acoustic guitar - one drumming on it, four others plucking the strings and strumming at the frets - has become a YouTube phenomenon of its own, picking up more than 28 million views in just the past fortnight. "I sit back with a curious smile over that," says Gotye.

"It's like a throwback to the Sixties where a local act could pip the original artist to the post in their market. I wish them all the best with the song - it's a clever, novelty cover. But I won't deny there's a part of my ego that really doesn't want their version to eclipse mine."

This "compact piece of drama wrapped in a pop song", as Gotye describes it, has now lost much of its negativity as its popularity has grown. "In concerts it's become a huge celebration experience. The audience has really taken it on, especially when Kimbra isn't there to sing her part. It's quite a reflective song so to have a large crowd screaming it back at you is quite weird." We'll get our chance next month at two London concerts, by which time it should have become the chart hit it deserves to be here too.

Born in Belgium as Wouter De Backer but an Australian resident from the age of two, the 31-year-old known as Wally has been releasing records with rock 'n' roll trio The Basics, and as sample-based electronic solo act Gotye (pronounced like the designer Jean-Paul Gaultier) for around a decade. He was a fairly minor, left-field musician with a couple of small hits at home until the release of this song.

If there are any aspiring musicians hoping that Gotye has stumbled upon a secret formula for hitmaking, he assures me that during this tune's gestation period he had no idea how special it really was. He worried that its downbeat mood was too similar to his 2006 song Heart's a Mess, the single that first brought him some lesser crossover success in Australia. "I thought existing fans would view the new one unfavourably by comparison."

And he certainly didn't write it as an attempt to storm the charts. "My last record [Like Drawing Blood from 2006] was self-released with zero marketing. All I thought was, 'If I can sell 1,500 copies of this in Australia I'll just make back the $15,000 I spent mixing it'. Maybe I can buy a new computer. But it sold pretty well, I found an audience and was able to start playing live. That felt like success to me.

"I'm proud that this song has weaselled its way through the more plastic pop tunes to the top of the charts on its own terms," he continues. "I look up to people like Kate Bush and Peter Gabriel, who always did their own thing and created their own sound world but still made music that appealed to lots of people."

There is odder stuff on Somebody That I Used to Know's parent album, Making Mirrors, that will surprise and intrigue those who become fans on the basis of a lone single. State of the Art is a song about the retro organ the Lowrey Cotillion sung in a deep, distorted robot voice. Eyes Wide Open samples the Winton Musical Fence, a giant art installation in the Queensland Outback. In concert you'll see him play the theremin and a MalletKAT, a kind of electronic marimba. It doesn't look like he'll phase out his more outre experiments now that the masses are looking in his direction.

"I'd like to make more pop music that can take on peculiar subjects but I realise that probably won't appeal as much as this song about a break-up. But that's fine - I'll follow my own direction and see what happens."

Somebody That I Used to Know is in the iTunes store now and gets a full release on Feb 6. The album Making Mirrors is released on Communion/Island on Feb 13. Gotye plays Wilton's Music Hall, E1, on Feb 13 (020 7702 2789, wiltons.org.uk) and the O2 Shepherd's Bush Empire, W12, on Feb 29, (0844 477 2000, o2shepherdsbushempire.co.uk).