Tupac's estate has finally begun talks with a potential buyer, but it's not for the XXX part … it's all about the music.

An anti-hangover drink company called NOHO has offered to pay $1,000,000 for the rights to the unreleased song 2Pac was rapping along with … while he was being "tended to" by a female in the 1991 footage.

Sources connected to the negotiations say the offer was big enough to catch the estate’s attention, because a rep for Pac's people reached out to NOHO and the two sides are trying to work out a deal.

There’s only one problem, the estate doesn’t have possession of the sex tape and aren’t even sure which song is playing on it.

We're told if the estate can’t get a hold of the tape, they have other unreleased Tupac songs they're willing to part with … if the price is right.