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'Pretty Little Liars' Star on "Devastating" Finale: "A" Reveal "Breaks Your Heart"

'Pretty Little Liars'  Eric McCandless/ABC Family

Sasha Pieterse tells THR she was "honestly shocked" when she learned what Ali would be doing after the show's five-year time jump.

Viewers may not feel quite the way they expect to once "A" is revealed on Tuesday's

The ABC Family drama's sixth season has centered on the girls and their hunt for Charles, who had previously trapped them in his lair. In last week's prom episode, Alison (Sasha Pieterse) cornered the mysterious evildoer, and he unmasked himself to her. 

that this week's game-changing finale will be "shocking" for viewers, who will have "a lot of mixed emotions" by the end.

"It's really dark, and you find out all these answers, but there's such a unique storyline there because you've never really seen what made 'A' tick, and you see that now," Pieterse says, emphasizing that the episode leaves "no questions unanswered."

She explains that fans may have trouble knowing who to root for, given the tough life that Charles has endured. "There's no right way to feel about it," she continues. "You don't want to feel anything for 'A' — you want to just be mad at 'A.' But at the same time, when you find out all these things that have happened to 'A' and this sad person, it breaks your heart." 

Pierterse, who points out that she was taken aback upon learning who "A" is, believes fans will be satisfied by the amount of familiarity they have with the culprit. "[Fans have] basically been saying they hope it's not someone that's too close to us, but at the same time, they hope that it's not someone that we've hardly seen," she says. "And I think that their wishes have basically come true."

After the finale, the season resumes in 2016 with its characters having made a five-year time jump, and Pieterse says viewers will want to brace themselves to learn Ali's new path. 

"I was honestly shocked when they told me what she's going to be up to in the time jump, but the more that I play it, the more I realize that it's right," the actress says, revealing that Ali "finds [normalcy] in a location that you wouldn't expect her to. It's been very fun for me to play."

, things won't be entirely hunky-dory for the Liars, even once they've left Rosewood High in the dust. "Many dark things" are in store for the girls in the next five years, according to Pieterse, who feels the jump has "reinvented" the series. 

"I think the fans are going to fall in love with [the show's new direction] exactly the way they did originally, but now that they know what happens in the past, it makes it that much more real and that much more devastating," she adds.

' season-six summer finale airs Tuesday at 8 p.m. on ABC Family. Share your final pick for Charles in the comments.

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