Hair metal's biggest hit song — Def Leppard's "Pour Some Sugar On Me" — shouldn't even exist. Fortunately, a series of unlikely events ultimately led to one of the biggest mainstream breakthroughs of any musical act in the 1980s.

Def Leppard had already made a name for themselves by the time they entered the studio to record the now historic 1987 album, Hysteria. But the success of the track that was a last-minute addition to an album already two-and-a-half-years in the making is what thrust the U.K. group to the peak of super stardom.

In the video below, we revisit those recording sessions as told by members of Def Leppard through interview clips across the decades. They also reveal the circumstances which gave way to the completion of "Pour Some Sugar on Me."

That signature opening riff? Producer Mutt Lange, a big country fan, introduced it to the band before they transformed it into something more biting and metallic. There was "almost like a violence to it," guitarist Phil Collen says of that riff once it was in his hands.

READ MORE: 11 Cheesiest Hair Metal Ballads

There's a lot more that went into it as well and, even after Hysteria was released, "Pour Some Sugar On Me" wasn't an immediate smash hit. Instead, thanks to a particular nightlife scene, it organically grew in popularity, suddenly being requested as fans called into local radio stations.

"From the day we started in '77, we wanted to be the biggest band in the world. And by the time that album came out and that tour kicked in, for a little while, we were," singer Joe Elliott remembers.

WATCH: Hair Metal's Biggest Hit Shouldn't Exist

Top 30 Hair Metal Albums

The 30 best hair metal albums of all time.

More From WGBF-FM