Brace yourselves, Beliebers: Justin Bieber has changed up -- and chopped! -- his hair.

The 16-year-old singer got a dramatic new haircut Monday on the set of a Rascal Flatts video, pics at TMZ revealed.

Although nervous about the hair-makeover, performed by his personal hairdresser Vanessa, the pop phenom said he "wanted to change it up."

The new look -- short on the sides and tousled on top and without the all-important "swoosh" -- is "kind of mature," Bieber mused.

Why did he do it?

"I got a lil haircut," the Never Say Never star tweeted later on Monday. "I like it...we are giving all the hair cut to CHARITY to auction. Details coming soon."

Tell Us: What do you think of Bieber's hair?