Duke Gadd's cause of death has been released ... the drummer died of an overdose of fentanyl and cocaine -- mirroring what ...

We spoke with Carol Gadd-- Duke's mom and wife of legendary Steely Dan drummer Steve Gadd ... and, she tells us they haven't ...

In his since-deleted Instagram post, the 53-year-old eighties icon had claimed the rocker had died from 'a fentanyl overdose,' which angered Carol Gadd who believed her son had died from a heart ...