Porn star Jesse Jane's official cause of death is an overdose ... TMZ has confirmed.

TMZ has learned Jesse died of an accidental fentanyl and cocaine overdose according to the Oklahoma City Medical Examiner's office.

We broke the story back in January ... law enforcement sources told us the famed adult film actress was found dead at a home in Moore, OK after authorities responded to the residence on a welfare check.

Jane was found dead in the house alongside her boyfriend, Brett Hasenmueller, and our sources told us it appeared to be a drug overdose at the time though the cause of death wasn't officially revealed until today.

Jane was one of the biggest porn stars during the 2000s ... appearing in some big-name porn films like "Pirates II: Stagnetti's Revenge" which reportedly cost more than $8 million to make.

She also made content for Playboy and hosted the AVN Awards -- the porn industry's version of the Oscars -- multiple times. She also appeared in mainstream shows and movies like "Starsky & Hutch," "Entourage," and "The Bad Girls Club."

Jane was 43.

RIP