Andrew McMahon is the voice of a generation—at least, he is for pop-punk die-hards in the early 2000s. This year marks two big anniversaries for the songwriter: Jack's Mannequin's debut album, Everything in Transit, turned 10 in August, and his first band Something Corporate's super-hard-to-find first album Ready...Break celebrated its 15th anniversary in September.

Even though a few of those songs were re-recorded for later albums—including "Drunk Girl" and "Cavanaugh Park"—one hidden track sticks out as the band's No. 1 fan favorite: "Konstantine." The 10-minute song is Andrew's most requested, even 15 years later as he tours with his new project Andrew McMahon in the Wilderness. Yet it's one he rarely plays. When we caught up with Andrew recently, he revealed the full history of the song—including how it was supposed to be half as long, who it's really about, and why he won't be playing it more than once a year.

Glamour: Ready… Break turns 15 this year, and that's the first version of "Konstantine" that fans heard. Do you remember when you wrote it?

Andrew McMahon: I do, and I don't. If it came out on that live EP, it was around the senior year of my high school, maybe that summerish. God, it's so hard to tell. Ready… Break came out in 2000 toward the end of the year, and I graduated that year. Most of the record had been completed around that summer, and then we did a live show at the Coach House. That's pretty wild, 15 years.

Glamour: Is Konstantine a real woman in your life?

AM: Yes and no. It was sort of a composite of a few people, truthfully, but with one very much leading the charge. I was in high school. I was dating a handful of different girls, which is a tricky thing to do when you're in high school, you know? [Laughs] To me, that song takes on this epic thing because it's what high school love is: super confusing. One day you think you see the rest of your life, and the next day, you're like, "I need to go meet this other person over here." But I was very caught up in the romance of this thing, and it took on this life of its own. I was trying to win an ex-girlfriend over at that concert that I think is on that recording, I'm pretty sure. I was free-versing all of those lyrics in the middle of the song. I had written so much and couldn't figure out what to include and what not to, so in the middle of the song I just dove into a million ideas. When we practiced it originally—what we were going to do that night—it was probably a four- or five-minute song. It had that breakdown, and I was going to do one of those lines, but instead I just did them all.