"I think it was just sheer boredom," the 36-year-old actor told ET's Cameron Mathison of his barely-there buzz cut, "that and the idea of a clean slate, a blank slate, and the new year. [I'm] starting things anew."
Pine sports a fuller head of hair in his upcoming film, Wonder Woman -- as well as a few extra pounds of muscle.
"I got in incredible shape for this film. I was also wearing about 75 pounds of clothing. [Wonder Woman director] Patty [Jenkins] has a fetish, you just like a lot of clothing. You like down coats, winter sweaters," he joked with Jenkins on the carpet. "What I realized is that I made a major mistake, I got in great shape and they just put clothes over all my hard work."
While his "hard work" was covered up by clothing, at the end of the day, Pine said that he's proud to have been a part of the upcoming super hero film.
"Really, there's obviously a narrative to be had about that. I just look at it that I got a chance to spend time with people I love with a story that I really, really, really... I just fell in love with it, and really, love is at the center of the film," he explained. "I think what Patty did so intelligently, was she married all these different genres and the beating heart of this film is a real love story, which I don't think we've seen in the superhero canon recently. I think it hearkens back to what Patty loved in the first Superman, and it's just a classic love story and a classic story done well."
Wonder Woman hits theaters on June 2.