The cast of 'Nashville' are (mostly) protecting the details of who Juliette's baby daddy is, but they're happy to talk about working alongside a very pregnant Hayden Panettiere.

Actor Jonathan Jackson (Avery Barkley) tells Taste of Country that Panettiere has always been professional, dedicated and gifted, and that hasn't changed since she started growing a bun in her oven.

“The only thing that’s changed is she has to lay down more often. Her feet are hurting," he says. “She brings it every day, so we have a good time working together."

Panettiere is due to deliver a baby girl in December.

That Jackson and Panettiere are working together could be a clue. Jackson admits he knows some of the details about how the baby drama will play out after Season 3 begins Wednesday (Sept. 24) at 10PM ET on ABC. They've filmed about seven episodes so far, but not every cast member has worked with the pregnant star. Sam Palladio (Gunnar Scott) hasn't worked with her yet. Chaley Rose (Zoey Dalton) was very careful not to say anything about the situation, although she did reveal what's in store for her character.

"She does have some anxiety about Gunnar and Scarlett," she says, "and this new girl that comes along. Gunnar's high school sweetheart."

About that new girl: Palladio says fans are really going to love that storyline. Alexa Vega will play Kiley, a single mother who is rumored to be raising Gunnar's son.

"I think viewers are going to be very excited when his old girlfriend comes back," Palladio reveals. "It opens up a lot of his past. It brings up a lot of emotional connection to his family and the loss that he's had through losing his brother, and so we start to see some heart to Gunnar and some of his fragility and some of how his childhood shaped who he is. And this girl was integral to that."

Jackson's Avery Barkley or label executive Jeff Fordham (Oliver Hudson) are the two most likely candidates to be Juliette's baby's father. However, one can never rule out a twist on a show like 'Nashville.' Jackson would only say that the first few episodes are very trying for his character. He's apparently "spiraling" after learning Juliette cheated on him.

“The arc of Season 2 was great, taking Avery from sort of a narcissistic guy who learns some humility and sort of became more mature," he shares. "But I think the betrayal of Juliette is sort of challenging that.”

All three actors talked after performing on the Grand Ole Opry stage on Tuesday night. Jackson's performance was remarkable because he chose a U2 song. He's a rock fan mostly, he says, although he grew up on a steady diet of country music. Rose also grew up country, while Palladio says he didn't know what the Opry was growing up in England. He's happy to be getting a quick lesson, as he lives and works in Music City.

All performers at the event were part of the 25th Anniversary of Country Cares for St. Jude celebration. A portion of ticket proceeds went directly to the St. Jude Children's Research Hospital.

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