Kmazur/WireImage; TwitterWhere in the world is Aaron Carter?
The 22-year-old pop singer is practically unrecognizable in photos he posted this weekend on Twitter.
With that in mind...
It got us thinking about some other Hollywood stars who drastically changed their physiques. While Carter hasn't revealed why he's muscled up, stars like Taylor Lautner, Jake Gyllenhaal and Christian Bale have transformed their bodies all in the name of show business.
From the ridiculously ripped to the shockingly skeletal, check out the incredible transformations in our Bodies of Work photo gallery.