Porn stud Mr. Marcus -- who, we kid you not, is a member of the porn Hall of Fame -- was arrested in Hollywood early this morning, after cops say he was driving drunk ... TMZ has learned.

Law enforcement tells us ... Mr. Marcus -- star of "Phat Ass White Booty 6" and "Manhammer 7" -- was pulled over in a Hyundai Elantra around 2:30 AM after cops noticed the car weaving all over the road.

During the stop, we're told cops smelled booze, so they performed a field sobriety test.

Sources tell us ... Marcus bombed the breathalyzer (blowing isn't really his forte) ... so he was arrested for DUI.

Marcus -- who was the source of the famous porn star syphilis scare of 2012 -- is still in custody.

Porn star Jessica Bangkok just got 86'd -- no, it's not a sexual position -- she got fired for letting a guy known to have had Syphilis have sex on her radio show.

Sources connected to Radio Sex -- a SiriusXM channel -- tell us Jessica, along with legendary porn stars Debi Diamond and Nicki Hunter all got the hook this week after the channel's owner launched an investigation into Jessica's show, "Real Life Stories."

The guy with the alleged STD is Mr. Marcus. Pics of his on-air sexual escapade surfaced on social media, and the suits at Manwin USA -- which owns Radio Sex -- went crazy.


We're told even though it's a sex show, no one is allowed to have sex in studio. Company policy not only prohibits it, they don't have the necessary permits to screw on air.

But an even bigger issue is the whole Syphilis thing. Mr. Marcus -- a porn star himself -- hid the fact he had the STD last year, and had sex with a bunch of porn stars. When word got out, the industry shut down for more than a month while everyone was tested.

The honchos at the radio station were livid that Jessica knew of Mr. Marcus' history yet let him do the dirty in studio. (To be clear, Marcus isn't accused of boning Jessica or the other porn stars in the studio. He's accused of banging a non-porn star guest he brought in.)

During their investigation, the honchos also discovered Debi and Nicki were doing sexual things on the air which is a big no-no. So they also got the axe.

In case you're a fan ... that's why all the shows have been in reruns this week.

Mr. Marcus has not returned our calls for comment.