TMZ broke the story ... Tupac received oral sex from a mystery woman back in 1991 ... and it was all caught on tape. The 5-minute video shows Tupac in a living room, holding a cocktail in one hand and a blunt in another.
An unreleased Tupac song is playing in the background, as the rapper sings along, wiggling his hips -- all the while getting serviced by the woman.
