Watch 'Nashville's' Lennon and Maisy Sing Acoustic, Talk Connie Britton's 'Legendary' Hair

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No surprise here: singing sisters Lennon and Maisy Stella were born to perform.

Before starring on Nashville, and way before becoming an online sensation with their viral cover of Robyn's "Call Your Girlfriend," the girls were coming up with future singles in the bathtub. Their new song "In the Waves" is available now on iTunes, and the lyrics serve as the basis for their children's book of the same  name. 

"We wrote the chorus of the song when I was about 8 [years old] and Maisy was 4-ish," Lennon, now 15, tells ET. "We went back and re-wrote some of the verses and the rest of the song to make it better than it was, cause we were so little... We wrote it in the bath, we were just singing our hearts away."

WATCH: Lennon and Maisy Cover Charli XCX and It's Amazing

The sweet children's song tells the story of two young sisters who use their imaginations to turn a regular bubble bath into a fun-filled beach adventure. Fans can see animated versions of Lennon and Maisy in the page of the book, but let's be honest -- you really just want to hear them sing, right? Check out an exclusive, acoustic performance of "In the Waves" in the player below.

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While it's all fun and games 'in the waves,' things are much more dramatic in the sisters' TV roles on ABC's Nashville. Season three of the hit soapy dramedy closed on a cliffhanger earlier this month. (As if we'd expect anything less!)

"You cannot be mad at us because we don't know what happened to Deacon!" teased Maisy, 11, the younger, and undeniably more animated, of the siblings. (Big sister Lennon affectionately calls her "dramatic.")

And while the girls don't have much intel (yet) on the show's upcoming fourth season, Maisy would very much like to stop seeing her sister lock lips on-screen.

"The only thing I don't want to see is her kissing any more boys and then I'm fine," Maisy declares, motioning to Lennon and adding a faux gagging noise for fun. "I'm like, 'OK, it's bathroom break when Lennon has to kiss Colt [actor Keean Johnson]... I'll go make the popcorn, guys, I'm done!'"

Can't say we blame the girl! In fact, Lennon says that she asks all her family members to stay far away on those days -- but that doesn't mean she's missing any guidance on-set.

"Chip [Charles Esten, who plays Deacon] has taught me everything that I have learned in this acting stuff," says Lennon. "One thing I always stick with that he showed me is before a big scene, whether you're crying or something emotional that you feel, like you have to lock into, if you go as far away as possible from that emotional before the scene it makes it so much easier to get into it after. You'd think you would have to cry before your scene, but it's actually easier if you laugh before. It's a weird thing, but it gets it so you have somewhere to go."

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If Lennon's scenes with her on-screen dad are any indication -- there must be a lot of laughter between takes.

And what about on-screen mom, Connie Britton? We couldn't help but ask for the inside scoop on that perfect, unbelievable hair.

"It's legendary," Maisy gushes. "We always make jokes with her, like we go to touch [it] and she goes, 'Not the hair! Not the hair! Not the hair!!!'"

Lennon, Maisy, Connie and her hair will be back on the small screen next fall for Nashville season four. Still itching for more? Click here to read ET's wide-ranging Q&A with Will Lexington himself, Chris Carmack.

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