Here’s Billy Joel’s rock-star genesis story. It’s in two parts, so pay attention.

Part one: He was 14, playing at a church teenage social in his native Long Island ’burbs in the early 1960s. It was the first gig for which he was paid, a whopping $15.

“It was at the Holy Family Church, a Catholic church. We did a bunch of covers. Beatles, Stones, instrumentals like the Ventures. And we were called ‘The Echoes.’ And I looked down and there was this girl who I had a crush on . . . and she’s looking at me, the first time she really looked at me, looked looked at me. I thought, ‘Wow, this is cool.’ ”

Part two: On tour in Knoxville, Tenn., about a decade later, he was in a hotel between shows. He had a reggae tune bouncing around his head, something about a hot chick, and he thought about that long-ago girl at the church social.

He’s telling this story on a recent morning in the office of 20th Century Cycles, his motorcycle garage/museum on a side street in this town an hour and change east of Gotham. The skies are gray-flat outside, it’s blustery and cold, the terminus of one line of the Long Island Rail Road just down the block. Now he leans forward in his straight-back chair, dropping into Jamaican patois, doing the song as he did it for his bandmates that day, with sound effects:

To understand what Billy Joel has meant to his fans, The Post's Neely Tucker suggests watching the Kennedy Center Honors recipient's performance of "Scenes From an Italian Restaurant" at Shea Stadium in 2008. (Tom LeGro and Neely Tucker/The Washington Post)

“Come out Virgin-ee-ah (chaka)/Don’t let me wait (cha cha)/You Catholic girl (stop) you wait much-a too late.”

When his drummer razzed him that “Billy, the closest you’ve come to Jamaica is Queens,” which is a pretty funny New York joke, he agreed and dropped the Caribbean rhythm. With Phil Ramone producing, “we made it a shuffle against a straight four beat.”

Ladies and gentlemen, we give you “Only the Good Die Young,” one of the many hits from “The Stranger,” the 1977 album that launched him from being an interesting young talent to an American icon.

“I never got Virginia,” he says now, “but I never forgot her, either. People thought that song was about the Catholic Church. Ha. It was about lust.”

Three decades after that epiphany, Joel has sold more than 150 million records, more than any other solo act save Garth Brooks and Elvis Presley, he’s in the Rock and Roll Hall of Fame, and is now a Kennedy Center honoree.

Piano Man,” “Just the Way You Are,” “Movin’ Out,” “New York State of Mind,” “Uptown Girl,” “It’s Still Rock and Roll to Me,” “Allentown,” “River of Dreams” — it’s the radio airplay of the 1970s, ’80s and early ’90s. More than three dozen hit singles in a 21 / 2-decade span. Albums that went platinum. Concerts that sold out in minutes.

If it has sometimes been difficult to be the rock star Billy Joel — three divorces, two stints in rehab, one youthful suicide attempt — the man himself now appears to be one of the more down-to-earth guys in the business.

“I think I’m pretty much a happy guy,” he says, then pauses. “Or a contented guy, anyway.”

He’s in a good mood this morning, a sweater and a watch cap on against the chill. A guy with a penchant for the catchy melody rather than the soul-searching epic, he’s witty, open, a good conversationalist.

He’ll look at you while you’re asking a question, his face flat and expressionless, and then look off and up to his right while starting his response, before looking you back in the eye. His speaking voice is just about like his singing one, resonant if not warm, but with more of a Long Island accent. He is famously loyal — to a fault in the case of a former brother-in-law (from his first marriage) and management team that took millions from him before he realized it — but doesn’t seem to hold grudges. He’s speaks fondly of Christie Brinkley, his supermodel second wife and mother of his beloved daughter, Alexa Ray.

If you were to drop by his house a few miles away in Sag Harbor on any given evening, he says, you’d probably find him cooking with his girlfriend Alexis Roderick, classical music on the stereo. He reads a lot, fascinated with history (he’s currently into William Manchester’s three-volume biography of Winston Churchill).

And after three decades of hosting question-and-answer sessions with college students interested in the music business, he’s about as approachable as it is possible for someone of his fame to be.

“He’s a very forgiving guy, he lets you f--- up and doesn’t beat you over the head with it,” says Steven Cohen, lighting director on his tours and one of his closest friends for four decades. “I’ve been there just about every song he’s written, he’d play them for us before anyone else. . . . He helped me bury my father. There’s a very close connection there.”

This year, Joel was doing one of those music classes at Vanderbilt University. A kid named Michael Pollack asked if he could accompany Joel on “New York State of Mind.” Joel has heard these sort of requests for years — he once kept a gong on stage to get rid of poseurs — but he shrugged and said, “Okay.”

Pollack was phenomenal and the video went viral. Still flabbergasted, Pollack says he’s getting writing gigs that he never would have otherwise.

“He created the opportunity for me to create a name for myself,” he says in a telephone interview. “He’s given me an entire new career path.”

Joel hasn’t released a pop album in 20 years — he says he got bored and boxed in by the format — but, since having both hips replaced, he’s back out on tour. Once the pop star critics loved to hate, he’s seen his career burnished by a growing affection and respect. The Kennedy Center recognition, he says, still has him “a little hornswoggled.”

None of this success came easy.

In 1949, he was born to a pair of Jewish immigrants, Howard and Rosalind Joel, in the Bronx. Dad came from Germany, Mom from England. Dad played classical piano, Mom sang Broadway show tunes and anything else.

But Dad “never really adjusted to life in America,” says Joel. Howard Joel was an engineer for General Electric and, after hours, a frustrated musician. In need of cheaper housing, the couple moved to a cookie-cutter ’burb on Long Island when Billy was a kid. On the surface, one might see a cheerfully modest life in this tableau — immigrant parents sharing a love of music, building a new life in the New World.

Instead, Howard Joel left the family and moved back to Europe, breaking off all contact with his son. His mom was forced to work as a bookkeeper and secretary to pay the bills.

“Most of my memories of him were — when he was home, he would play classical music. Chopin, or Beethoven sonatas or Debussy. We had an old upright piano. It was this old piece of junk. A lot of the keys didn’t work, so it was tough to play the thing. It was more a garden ornament than it was a piano.

“I’d be listening [to him playing] in the other room thinking ‘Wow, that’s beautiful,’ but he’d walk out of the room in a very dark mood. He was never happy with his musicianship. He wasn’t good enough. He wasn’t what he wanted to be. . . . Now, at this time of my life, I understand. You run into the wall of your own limitations, and you wish you could do more, you want to do more, you wish you had studied more, and that happens. You really get in a dark mood.”

Once, in the early 1970s, he looked up his father while he was on a tour of Europe. The record company people sent Joel a telex that they had located him on the very last day of the tour. When Joel was back home in Los Angeles, he called the old man, who eventually came to visit. They had a relationship over the years, but nothing much came of it.

“We never got all that close.”

It’s tough, your dad walking out. You’re left with abandonment issues, with longing, with the musical gumbo of your youth — the Four Seasons, the Beatles, Bill Evans, Ray Charles — and you make the best music and the best life you can.

You want to appreciate the man’s accomplishment? Billy Joel never really learned to read music. Does it all by ear. Can’t score a single tune.

The definitive show

Let’s see if people still love him. Let’s look at the “Last Play at Shea” concert, the two-night set that closed the historic stadium in 2008.

Late in the show, Joel hit the first trickling notes of “Scenes from an Italian Restaurant.” It’s arguably the one song in his catalogue that no one else could have written — a seven-minute, three-act mini opera from “The Stranger.”

The song is about old friends meeting for dinner and reminiscing about Brenda and Eddie, a pair of Long Island high-school sweethearts. Never released as a single, it has long been a cult classic to his fans.

From the very first line — “A bottle of white, a bottle of red” — the massive crowd is not singing along with him, they’re bellowing, a vast, spine-tingling chant coming from the upper and lower decks, the field, everywhere, a sort of humming throb of the universe.

When the song kicks into its second act — the tempo gets giddy, like a carnival ride — Joel does a very small, very magical thing. He changes one word.

As written, the exuberant line is “Cold beer/hot lights/my sweet romantic teenage nights.” But on this night, as he has no doubt done often, he changes it to “our sweet romantic teenage nights.”

You, me, we, us.

From then on, it’s not really even a song anymore. It’s some sort of cathartic mass-performed communal ritual, a tribal, pagan thing — 55,000 people screaming into the Long Island night about Brenda and Eddie and they can’t tell you more than they told you already and the man on the stage is holding sway over them all, fingers dancing over the keys, alive, electric, swaying, his stadium, his home, his people, his song, and you’d swear the entire stadium just rose 15 feet in the air and held there, levitating.

Billy Joel, at the piano. Man.