VIDEO: 'Pretty Little Liars' Costume Closet Revealed: How Spencer, Aria, Hanna and Emily Get Their Bold Looks


"Pretty Little Liars," the smash hit show on ABC Family that thrives on untangling dark secrets, took "Nightline" on a special tour through the show's costume trailer, revealing how the signature looks for the four main characters were developed.

Mandi Line, the show's costume designer, moved through racks upon racks of purses, graphic Ts, blouses, mini-skirts and other clothes belonging to Spencer (Troian Bellisario), Aria (Lucy Hale), Hanna (Ashley Benson) and Emily (Shay Mitchell), describing each of the girl's pieces as she went.

"Spencer, the girl with more brown belts than I've even seen in stores, she's got every kind of preppy, upscale, chic, classic belt," Line said, moving through the clothes set aside for Bellisario's character. "You won't find any studs in this line. No studs. That belongs to Aria."

For Aria, Line mixes girly glam with an edge, and piles on the accessories: bold earrings, studded rings and chunky bracelets.

"I think her accessories weigh more than she does. That poor girl, I throw everything on her," Line said. "I based Aria after my childhood, a fantasy of a girl I was never allowed to be or didn't have the means to have all this. … She's the kind of girl that can throw everything on at once, and you're like, 'How did she do that so awesome?'"

To say "Pretty Little Liars" has a huge fan base is an understatement. It's the most tweeted about show in television history, drawing on the power of Twitter, Instagram and other social media outlets. The stars constantly tweet and engage with fans, most of which are young girls and teens like the show's characters, so it's no surprise that fans look to their favorite characters for fashion ideas.

"Emily's a little bit more B-Boy this season. She's gotten a little more thug," Line said, pointing to Mitchell's set of clothes. "She's the girl that if she's going to do a dress, she's going to do a jersey dress. … She does the perfect mix of the feminine and tomboy. It's funny because you would think that I would hear mostly about the fashion from the fans of the other girls, and I hear so much about Emily going, 'I didn't know how to dress. I'm sporty, and I didn't know how to glam it up.'"

Often Line will be playful with the girls' outfits, such as a pastel rainbow cropped faux leather jacket for Aria when she went to a funeral home in season 4, episode 14, and an ice cream-print "Happy Ashley" blouse that Line called "one of our favorites" from last season.

"Hanna, we always say she's the one that pulls off all the bright colors, so she's got the feminine, she's got the flowers," Line said. "The 'Happy Ashley' shirt, I knew this was going to be a good one, and one episode, Spencer borrowed it, and it was so funny because it couldn't have been less Spencer. She was like, 'Oh, I had to borrow some of … Hanna's clothes,' so we made sure it was over the top."

Watch the full story about the "Pretty Little Liars" cast on "Nightline" TONIGHT at 12:35 a.m. ET.