The lead star from the FX series 'The Assassination of Gianni Versace' -- a role that won him tons of accolades this past awards season -- took the stage early Saturday morning at Tramp Stamp Granny's in Hollywood ... a piano bar that he has an ownership stake in.
Check it out ... Darren takes on the role of Bradley Cooper with the first verse and does pretty damn well. Then, a female companion gets onstage for Gaga's verse ... and absolutely kills it. We're told Darren went on to sing "A Whole New World" too, all impromptu.
It's been about three months since the Academy Awards wrapped up, where "Shallow" won Best Original Song ... but people still seem to be completely enamored with the movie, and the tune.
Take it away, guys!