The former Nickelodeon star was dressed in all black during a coffee run in Los Angeles Monday afternoon, and you can see why he's playing Elvis in the upcoming biopic ... Austin's pretty much a dead ringer for the King of Rock 'n' Roll.

Austin's always kinda had the Elvis look going for him ... and now that he's been tabbed by director Baz Luhrmann to bring the icon to life on the big screen, Vanessa Hudgens' boyfriend somehow looks even more like a hound dog.

Drake Bell told us last week Austin's got a good face for Elvis ... and Butler's got us all shook up as he slips even further into character.