Giorgio Armani died Thursday … and among those mourning the loss is a Hollywood icon who tells TMZ the legendary fashion designer helped make one of his films an instant classic.

As you know … Giorgio died “peacefully” at home surrounded by his loved ones. He was 91.

Paul Schrader, writer and director of “American Gigolo,” tells TMZ … the 1980 film starring Richard Gere had an unintentional cross-promotion that helped make the movie a classic … and pushed Armani’s lucky break into the U.S. market.

John Travolta was originally going to star in “Gigolo” … and it was his manager who suggested Armani for the costuming, since the studio wanted to get away from the looks of “Saturday Night Fever” and “Grease.”

Paul tells us … he and John met Giorgio in Milan, Italy and he agreed to do the film. After Travolta dropped out for personal reasons, they had to redo the entire wardrobe when Richard Gere was recast as the lead.

Gere himself tells TMZ … “Giorgio was certainly an original. An artist. A visionary of sorts. With the eyes and hand of a craftsman, and the soul of a painter. His work had his essence all over it. And he cared right up to the end. Uncompromising. I know there were those who he terrified because of his exacting nature. To me he was a supremely talented pussycat.”

Paul Schrader tells us they wanted to make L.A. “look and feel classy” … and after meeting the designer — already insanely popular in Italy — the director believed Armani would do that.

The film was a smash hit at the box office and with critics … and Giorgio used that to catapult the brand into the U.S. market — subsequently costuming several other films, including “The Untouchables” and “Goodfellas.”