Aussie DJ Bragged About Royal Prank ... BEFORE Nurse Suicide

The Australian DJ who pretended to be Queen Elizabeth II in a prank phone call ... BRAGGED about her accomplishment on Facebook ... right before the nurse who answered the call committed suicide.

TMZ obtained a screenshot of Mel Greig's Fbook page taken Friday evening in Australia ... a.k.a. BEFORE news broke that Jacintha Saldanha -- the nurse duped by Greig and her co-host -- had been found dead in London.

The post reads ... "Why is it that I can impersonate the queen to get private royal information but no one believes I'm the queen for a free champagne whilst out?"

Greig attached a pic to the post -- of herself and another chick, smiling and hanging out at a bar.

We reached out to Mel's rep for comment ... who said (again), "No one could have ever predicted the tragic sequence of events that followed the prank call."

As TMZ previously reported ... Greig and her co-host Michael Christian shut down their Facebook and Twitter pages immediately after the nurse's death -- and suspended their gig at the station.