Though he might have filmed his appearance on Wednesday, Justin Bieber's Late Show With David Letterman interview and performance aired last night ... and it was INCREDIBLE!

The Biebs has definitely come a long way since his first time performing Boyfriend and it seems that he's finally comfortable with the single on stage!

Check out Justin swaggin' all over the Late Show stage and showing off his NEW (Selena?!) tattoo in the clips (above)!!!

Justin and Letterman -- or "Grandpa" as Bieber refers to him as -- also covered everything from Justin's trip around the world, how he celebrated turning 18, graduating high school AND his Canadian citizenship! LOLz!

Take a look at some more clips from his appearance... AFTER THE JUMP!

Justin on singing opera:

The Biebs talks graduation:

Justin on turning 18 and voting: