You've heard this story a million times about some enormous hit song: "It was a last-minute add to the album," "It almost didn't make the cut," "We didn't think it sounded finished," "I wrote it in two minutes on my way to rehearsal," "I almost gave it to another singer."

And sure enough, one of last year's most inescapable songs, and one of the biggest hits in Beyoncé's already smash-heavy career, "Irreplaceable," almost didn't happen. Written by Ne-Yo and super-producers Stargate, the Record of the Year [article id="1575921"]Grammy nominee[/article] is the kind of tune that worms its way into your head and keeps you humming the hook, "To the left, to the left."

"Nobody expected it to be the phenomenon it was, it surprised everyone," said Tor Hermansen, one-half of the Norwegian production duo Stargate (his partner is Mikkel Eriksen). "For one, it crosses every boundary; it went from the mix show on Hot 97 in New York to country stations [courtesy of a collaboration with Sugarland at the American Music Awards], and it's a song people from all walks of life can enjoy." Hermansen also said the sound is so different — using a combination of a classic chord progression on an acoustic guitar, a modern-sounding 808 drumbeat and cellos — that it could have doomed the song to not fit any formats. But instead, the unique combination made "Irreplaceable" stand out from everything else on the radio and helped it grab the #1 spot on four different Billboard charts.

"We focused on the sound when we did it, and when we wrote it with Ne-Yo it was done first with a male vocal, and we thought, 'This is more of a female vocal part,' " Hermansen said. "We liked it and so did Ne-Yo, but he said, 'Who will cut this?' "

The tune was not specifically written for Beyoncé — in fact, Ne-Yo wrote it from a male perspective — and Hermansen said that had they been writing for the former Destiny's Child leader, they might not have gone in the direction they did. The sound just wasn't one they associated with her voice. Ne-Yo has said in interviews that he had Faith Hill and Shania Twain in mind when he wrote "Irreplaceable" as a country song, and Hermansen still thinks the tune could easily have been a country radio hit.

But once Beyoncé heard it, she loved it and was sure she could make it her own. "What happens sometimes, is you think about a specific artist and you put them in this box, the song has to be this way or that, and then you're usually confining yourself to the thing they did three years ago," Hermansen said. "But she heard it and did her own vocal arrangements, asked for a few changes to be made and some new drums, and she sang it much higher than the demo."

Once the sessions wrapped for "Irreplaceable," Hermansen said everyone felt they had captured something special and that Beyoncé had done the track justice, but there were still concerns that urban radio might not play the song because it featured acoustic guitars and was too pop. "But then it became the biggest urban record ... ever," he said.

When it was released in late 2006, "Irreplaceable" also helped take some of the sting out of the mixed reaction to the frantic second single from B'Day, "Ring the Alarm." Topping the Billboard Hot 100 chart for 10 weeks in 2007, "Irreplaceable" became an empowerment anthem thanks to a [article id="1568975"]nighttime-soap-worthy video[/article] in which Beyoncé kicks her philandering boyfriend to the curb.

"I love 'Irreplaceable,' " B told MTV News shortly after the song's release. "I think it's important to have those songs. I've had so many people come up to me in tears, saying, 'I experienced my first breakup. If it wasn't for the song, I wouldn't be strong enough to not call. I wouldn't know how much I'm worth.' I'm happy to be a part of that."

Coming off the emotional turmoil she conjured for her role as Deena Jones in the Oscar-nominated "Dreamgirls," Ne-Yo said the song helped Beyoncé work out some issues. "She had some stuff that she wanted to get off her chest, and that's what she did," he said. "An artist's art really only has to make sense to the artist, and if the rest of the world catches on, that's cool too. If they don't, hey, 'This is my art, leave me alone.' "

But it didn't take long for "Irreplaceable" to shoot B'Day back up the charts. The album, which had debuted at #1 with sales of 541,000, had nearly slipped out of the top 20 just six weeks later, but then climbed back into the top 10 three weeks after "Irreplaceable" was released.

To date, the song has sold more than 3 million digital copies and has become the best-charting single of Beyoncé's solo career.

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