Incredible make-up work!
Tyrone Power seems to age from about 19 to 59 in this movie, totally believably. He seems to be playing not Dorian Gray, but his portrait.
Kudos to Power for fighting to get this unsympathetic part, and to Ben Nye, the make-up guy for the film. This wasn't the sort of film that wins Oscars, and I don't think the category even existed back then, but Nye's work here is fantastic and subtle -- fully award-worthy, imo.