1. Sara Shepard was working as a ghostwriter at Alloy, the juggernaut book publisher behind Gossip Girl, when she came up with the idea for the Pretty Little Liars book series: Four friends trying to move on after the disappearance of their group's queen bee. Shepard revealed that she was inspired by two women she knew who had been kidnapped. "So I was always afraid of being kidnapped," she explained to Cosmopolitan. "I remember thinking, What happens when somebody takes you? What happens next?"
2. In a move that surprised Shepard, I. Marlene King decided to condense the plot of the first book into just the pilot episode. But it set the tone for the series' breakneck pace moving forward. "Sara Shepard writes these great OMG, WTF cliffhanger chapter endings," King explained to Cosmo. "I decided that if we could end each one of our episodes in a way that Sara ended her chapters—that was the tone I set out to accomplish. I knew the book fans would follow the material to television."
3. The first Liar cast was Lucy Hale, who didn't have to audition after forming a relationship with the studio through the short-lived CW series Privileged and "had a big following," according to King. But Hale was initially drawn to a different character, telling Cosmo, "I was very intrigued by Aria but I also loved Hanna; that type of character was one I hadn't tackled before."
To help find the best fit for Hale, King continued, "We started [pairing] her with some different guys for chemistry reads and that's when she realized she really wanted to be Aria."
4. Though she originally auditioned for Spencer, Shay Mitchell almost lost the role of Emily to another actress. "We had a really hard time finding Emily," King admitted to Cosmo. "We saw two [actors] on videotape, and I was inclined to go with the other person. But in the room, Shay just owned the character of Emily. She changed our minds in the room and got the role."
5. Troian Bellisario didn't think she was a good fit for Spencer, who was a little different in the original script: "The scene I auditioned with was her sneaking out of dinner with her family to smoke a cigarette with her sister's fiancé, which ended up not being in the pilot because it was too risqué!"
6. That cigarette-smoking scene ended up being one of King's biggest fights with the studio. "The biggest debate was [over] Wren smoking a cigarette!," King she told Cosmo, citing a Disney policy that frowns on people smoking. "But they allowed us to let him put out the cigarette butt in a plant holder. That was the most daring thing we did."
7. Janel Parrish revealed she originally auditioned for Spencer. "I got a few callbacks and then didn't book it," she told Just Jared Jr. "I remember being super bummed because I loved the script. But, about a month later they called me in for Mona and that was it. I'm super happy about that, though. I fell in love with playing Mona."
8. Sasha Pieterse, who would go on to play Alison DiLaurentis, was this close to landing the role of Hanna before producers discovered she was only 12 years old. "I knew what Hanna was going to do and I was like, 'Do we really want a 12-year-old doing those things?'" King recalled in an interview with Variety. "But also, they can only work a certain amount of hours under the age of 16. So that's when we just said she's Alison. She read with a few of the girls as Alison, she was several years younger than all of them, but she scared the hell out of everyone in a good way."
9. Ashley Benson was the last of the four main actors cast, with King revealing to Variety, "I remember her coming in for her audition and she was in tears because she was on a show called Eastwick and she had just found out it was canceled, and so she came over to this audition."
King continued, "We knew we wanted a blonde for this role because it was one of the last roles to cast and other than Alison, we did not have a blonde in the show. We couldn't find the right person and she came in...there's just something magical that happens with her and the way the camera captures her and those eyes. We all knew in the room that we found our Hanna."
10. PLL's theme song—"Secret" by The Pierces—was suggested by Benson after she discovered it while filming the pilot. As Bellisario recalled to Benson, "You were like, 'I want to show it to Marlene because I really think it could be a great theme song.'"
11. Aria's iconic shush pose in the first promos "was actually a spur-of-the-moment idea that happened to make the final cut," Hale revealed to Cosmo. She once tweeted her issue with the move, writing, "Hey has anyone noticed how my finger isn't centered when I am 'shhing' the camera in the intro? Yeah, it annoys me too."
12. The first photoshoot featuring the four main stars covered in dirt in a graveyard was so memorable that "many people thought the show was called Dirty Little Liars" during the first season, according to King.
13. While Keegan Allen's turn as Toby turned the character into a fan-favorite, James Neate actually originated the role in the pilot. He wasn't the only recast to go down during the series' run: Drew Van Acker took over the part of Jason DiLaurentis from Parker Bagley in season two.
14. In the books, Toby died by suicide, and King had intended to kill off the TV character in season one. But after seeing the fan reaction to Allen and the response to the Spencer-Toby pairing, she changed her mind.
15. Given that most of her scenes in the earlier seasons were flashbacks, Pieterse had to spend a lot of time in the same item of clothing: Alison's ruffled yellow tank. "I personally hate that shirt and have from the beginning," the actress admitted on The Talk in 2016. "There are 13 copies of that shirt, and I want to take all of them and like burn them."
16. Kylie Jenner, who often tweeted about watching the show, was invited to appear as a guest star in 2015, but the role never came to fruition due to an argument between Kylie and momager Kris Jenner, as documented in an episode of Keeping Up With the Kardashians.
17. Since its premiered in 2010, PLL was consistently one of the most buzzed about shows on social media and its series finale was the most tweeted about episode of television in 2017.
18. Known for its crazy twists and shocking reveals that often made no sense, the cast and crew learned to not ask questions. Literally. "I created a little box that hung on the wall in the art department," production designer Jakub Durkoth told Cosmo. "If you asked a logic question, you had to put a dollar in it."
19. After a breakup early in their relationship, Patrick J. Adams secured a small role on Pretty Little Liars to win back Bellisario. "[It was] a part that, at that point in my career, I would not have typically gone out for, because it was like, one day of work, on Pretty Little Liars,'" he told PopSugar. "I wanted her back, and so I went after that part with the full force of every single person that works for me in the industry. I had everyone on the phone, calling, saying, 'We're going to get this part, we're going to get this part.' I prepared for this Pretty Little Liars audition more than I've prepared for anything in my life."
His hard work paid off as the Suits star landed the season two role and the couple reconciled and got married in 2016.
20. While several characters were shown to be "A" over the years, "A.D." (a.k.a. "Uber A") was finally revealed in the series finale to be (spoiler alert!) Spencer's secret twin sister Alex Drake, played by Bellisario. And in an interview with Elle, the star revealed she had been spilling the secret for years after learning of the twist in season five.
"For a long time, people would ask, ‘Who's A.D.?' And I'd say, 'It's me!' And everyone would just laugh," she said. "It's kind of great when you have a secret that so few people—only me, Marlene, and a handful of others at that point—know. It means you can hide in plain sight."
21. PLL launched two shortlived spinoffs—Ravenswood and The Perfectionists—followed by a reboot last summer. Riverdale creator Roberto Aguirre-Sacasa is the mastermind behind Pretty Little Liars: Original Sin, which is set within the existing universe but focuses on a new group of liars tormented by a different version of "A."
22. In 2016, the six female leads got matching index finger tattoos to honor the end of Pretty Little Liars. "This happened," Hale captioned a photo of the group on Instagram. "Thank you @shamrocksocialclub for taking care of us. We couldn't not get tattoos to commemorate the show! And obviously on our 'shh' finger."