Exclusive | Why Billy Joel always wore a jacket and tie on stage –

HBO’s revealing new documentary on Billy Joel delves into the rocker’s personal life and career, from his beginnings as a struggling cocktail lounge “Piano Man” to selling out Madison Square Garden more than 100 times during an unprecedented decade-long residency.

But one topic the comprehensive five-hour project, “And So It Goes” by Emmy winners Susan Lacy and Jessica Levin, doesn’t address is how Joel went from a scruffy aspiring metal head in a cacophonous act called Attila to an angry young man whose public uniform was a coat and tie with a button-down and sneakers.

On the 1970 cover of Attila’s sole, ill-fated album, a long-haired Joel and his bandmate Jon Small wore furry barbarian costumes from the film “Ben-Hur” surrounded by hanging meat.

But soon after, Joel wouldn’t be caught without a coat and tie.

In 1976, Joel appeared on the cover of his solo album, “Turnstiles,” in the look that would define his career: a white dress shirt and a preppy rep tie.

The style was repeated on the moody covers of Joel’s breakthrough “The Stranger” (featuring Joel in a suit on a bed) and “52nd Street,” for which Joel paired the jacket and tie with prepster kicks Tretorns as he leaned moodily against a wall with a trumpet.

And while Joel may have been wearing a leather motorcycle jacket as he threw a rock at his own luxe home on the cover of his rebellious 1980 smash, “Glass Houses,” he appeared on the back cover pouting through a broken window in a preppy jacket and tie.

(Joel’s never seen in the doc on stage in any year without a signature blazer.)

Those close to the star tell us that the “Uptown Girl” singer hatched the hip buttoned up look with help from his first wife and manager, Elizabeth Weber (who gets her due in the doc for making Joel’s career).

The coat and tie was also perhaps a way to amplify his apparent disdain for costumed rockers of the day (a la Elton John), and also a way for the Long Island regular Joe (regular Joel?) to show some respect to his paying fans.

A longtime Joel insider told us when we wondered about the genesis of the signature look: “The origin of the look was simple… Billy said at the time the audience paid good money to see him — the least he could do was dress nice for them! And to him, that was a coat and tie.”

The doc also points out how the singer was a fan of (well-dressed) legends like Frank Sinatra and Tony Bennett.

In his 1974 tune, “The Entertainer,” Joel makes fun of showy performers wearing “all kinds of sparkles.”

Joel also bristles early in his career in an interview at being compared to over-the-top Elton, saying their styles were the antitheses of each other. (The rockers later toured together, and have been on and off frenemies over the years.)

Another force behind the look was the stylish Weber. (The doc suggests she could’ve been the character in that “Halston dress” with those “friends at Elaine’s” in Joel’s scathing hit “Big Shot”).

Our insider says, “The jackets were an evolution… Elizabeth picked them [for Billy] in the early years,” including an orange number Joel wore on the cover of his 1980 single “It’s Still Rock and Roll to Me.”

Top graphic designer Paula Scher is also credited with being instrumental in the creation of Joel’s album covers.