Billy Joel Ex-Manager Insists Biopic Isn't Trying to Defame Singer

Billy Joel's ex-manager says he tried early on to get the music legend to read the biopic script ... insisting he never tried to sneak the project past Billy.

Irwin Mazur -- the central figure behind the "Billy and Me" project -- tells TMZ he spent the last year trying to arrange a meeting with the "Piano Man" before the backlash surrounding the film reached a fever pitch.

Mazur insists there's "nothing defamatory" in the script and nothing he wouldn’t stand behind ... arguing it simply tells the story of their early days together, which he is very proud of.

The movie has already sparked serious controversy after Billy's camp publicly condemned it as "misguided" ... but Irwin -- who discovered Billy way back in 1966 -- says the project was always intended to focus on his experiences managing a young Billy during his days with The Hassles, before Columbia Records signed him in 1973.

Mazur also insists the filmmakers never planned to use Billy's iconic songs ... explaining the script centers around Billy's "cover band" era with The Hassles, before he became a global superstar.