AJ Michalka, Aly Michalka AJ Michalka, Aly Michalka

Although Hellcats' Marty (Aly Michalka) has been searching for information about her father, when the series returns on Tuesday, she'll get more than she bargained for: a sister.

And who better to play star 's on-screen sis than her real-life sibling AJ Michalka. "It was kind of a no-brainer, you would think, [but] you don't see siblings play siblings ever," AJ tells TVGuide.com.

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AJ plays Deirdre, who Marty meets while searching for clues about her father at a record store he used to frequent. Although Deirdre's skittish nature signals that there's more to her story than she's revealing, it takes some time for Marty to make the connection. "She can't hold it in for much longer," AJ says. "When Marty finds out, it is a relief for Deirdre because that's such a big thing in her life to know she has a sister."

Like in real life, the two share a love for music on-screen. (Aly and AJ have a band called 78Violet.)  "We play an amazing cover of "Mississippi" by Bob Dylan that was probably the coolest thing to play on the show," AJ says. "Our characters embrace each other the most when we're playing, and that's why "Mississippi" plays such a poignant role in the episode."

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Aly says that although Marty and Deidre are comfortable on stage together, it's a bit awkward when the curtain comes down. "It's not necessarily this connection of, 'Yay! Best friends!'" Aly says. "It's kind of scary." Adds AJ: "I don't think they realize how much they're alike or how much of a connection they [have}."

Watch full episodes of Hellcats in our Online Video Guide

While getting to know her new sister, Marty also learns some hard truths about her absentee father: Rex wasn't a rock star touring the world, but instead a destructive addict who never came around because he was high. Marty pours her heart out to her best friend, Dan (Matt Barr). Aly says filming the difficult scene actually helped her deal with some issues of her own.

"It was intense," Aly says. "At the end of the day, I was exhausted. I was going through some weird stuff in my own life personally, so to tap into those feelings for that scene was therapeutic in a strange way. It really shows this vulnerable side to Marty that's really broken inside."

Hellcats airs Tuesdays at 9/8c on CW. Are you looking forward to seeing the sisters act together?