Credit: Photo via Justin Bieber's Twitter Photo: Justin Bieber Shows Off His Bod in Shirtless Pic

We know Justin Bieber posts shirtless photos all the time — sending teens around the world into a tizzy of Bieber Fever symptoms — but we couldn't help but notice something different about his recent half-naked pic. The 18-year-old singing sensation is beefing up!

The "Never Say Never" singer took to Twitter yesterday (November 5), showing off his sudden six-pack and — dare we say — chiseled biceps, writing, "Me and @nickdemoura dance rehearsal get ready #watchout."

Oh, we're sure there are plenty of young ladies intently watching out after this skin-baring pic.

What do you think of Justin's (new?) ripped bod? Is he hitting the weight room too hard, or are you Beliebing in his bulked-up look? Let us know in the reaction buttons below.

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Source: @justinbieber

Follow Alissa Kombert on Twitter @AyeKayArt.