Cardi B's Live 'Sex Video' with Offset Isn't Real (UPDATE)

10:55 AM PT -- A rep for Cardi tells TMZ, the "sex video" isn't real ... it was all a joke. We're told they weren't actually banging, and were fully clothed in the video.

Cardi B doesn't seem to care about cheating rumors going around about her fiance Offset, because she just posted what REALLY looks like a live sex video of the two of them.

A video of what appears to be Cardi and Offset doing it doggy style -- which reportedly 1st aired on Cardi's Instagram Live -- has surfaced online. In the clip, Cardi says, "I don't got no more in me left. You gotta give a whole hour" ... as Offset's back there thrusting away.

Unclear if what they're doing is real or not -- you can't see the bottom half here, but it sure looks like they're banging. That seems to be what they want people to think, anyway.

I still put the pussy on offset 🤷🏽‍♀️Bartier Cardi

@iamcardib

Offset made some headlines this weekend after video allegedly belonging to him leaked, showing off a naked woman that many people said wasn't Cardi. She appeared to laugh that off though, saying she was still banging him.

Assuming this is what we think it is ... clearly.