Milli Vanilli Comeback?

The DJ in question -- named The Alchemist -- dropped the bombshell in L.A. recently .. telling TMZ, "I'm working on a joint with Vanilli ... Vanilli making a comeback."

And according to the Alchemist, Vanilli -- real name Fab Morvan -- is bringing his real voice to the recording sessions, adding, it's "real sh*t dude."�

We spoke with Vanilli's rep -- who tells us Fab is DEFINITELY serious about his comeback ... and has recently worked with DJ Tiesto ... one of the biggest DJs in the world.