The Bellas traded an a cappella tune for the LSU Tiger Marching Band’s pregame song, the stage for Tiger Stadium.

It happened on a Saturday during the 2011 filming of “Pitch Perfect,” and Shelley Regner made it happen.

Regner is the Baton Rouge actress who plays Ashley. Or is it Jessica? Anna Kendrick as Beca can never remember who is who, and she says as much while hanging in a tree in “Pitch Perfect 2.”

That’s the running joke in both movies. Ashley

and Jessica, played by Kelley Jakle, are the two girls who are always in the background, yet, as Ashley declares in the first movie, “We were here the whole time.”

And when watching “Pitch Perfect 2,” audiences will see Regner as Ashley in every scene with the Bellas. But what they won’t see is how the real life Regner served as her fellow castmates’ Baton Rouge tour guide during both filmings to the point of introducing them to LSU football in 2011.

“The filming was in the fall that year, and when it’s fall in Baton Rouge, it’s about LSU football,” Regner says. “I brought them tailgating, and I brought them to a game. They were overwhelmed — I don’t know what they expected, but they had never seen anything like that. They loved it.”

Welcome to Baton Rouge, Bellas. Twice.

The first movie had the Bellas, a competitive collegiate a cappella singing group, winning the national title. Two more national titles later, the second film advances them to the world competition.

And Regner, as Ashley, is with them at every turn. She now resides in Los Angles but was living in her native Baton Rouge when she answered an email for an open call audition.

“I had just graduated from LSU with a degree in theater in 2011, and I was put on this film as a local hire,” Regner says. “I didn’t realize what I was auditioning for. I sang a song for the casting director.”

And the song?

“It was Whitney Houston’s ‘I Wanna to Dance With Somebody,’” Regner says, laughing. “They just told us to sing our favorite karaoke song.”

She laughs again. Who’d have ever thought karaoke could lead to a place in the lead cast, one that would feature Regner’s photo in the main credits at the end of the second film?

And she wasn’t even thinking about a possible sequel when belting out her Houston favorite in the initial audition. She was competing against 70 other actors and assumed it was for a background role, something seen in passing.

Then she was called back, then again. And she was asked to sing and dance on the third callback.

“Then they called me on a Friday night and told me they wanted me to play Ashley,” Regner says. “All I knew was that I would be a character in a group of girls who sing a cappella.”

She didn’t learn that her castmates would include Kendrick, Rebel Wilson, Brittany Snow and Anna Camp until reporting to the set on the following Monday.

They became more than actors on a set, names on a screen. They became her friends, her family.

“I went to a fundraising event at an art gallery for Brittany Snow’s charity, ‘Love is Louder,’ last night,” Regner says. “I’ll be seeing a lot of the cast at the premiere tomorrow night. It’s nice, because we’re all out in L.A.”

Regner spoke on the morning before the movie’s May 5 premiere in Los Angeles. She spent that afternoon shopping for a dress for the event, where she met up with her fellow Bellas.

The same Bellas she showed around Baton Rouge during the first filming. She was the hometown girl, so she could point them to all of the good gathering places, the best places to eat and, of course, to Tiger Stadium.

“It was a great experience for them,” Regner says. “They had no idea that this went on in Baton Rouge.”

When the Bellas reunited in Baton Rouge in 2014, things were different. Filming took place during the summer and a different director was at the helm.

Jason Moore directed the first movie. Actress Elizabeth Banks took over the director’s chair for the second. She produced both movies and starred as Gail, the sharp-tongued television commentator.

“Liz was such a joy to work with, and she was so passionate about this project,” Regner says. “There was one point when we were filming at Camp Istrouma that we all jumped into the water and formed a circle, then joined hands and counted, “One, two, three, Aaaahhhh.’ She didn’t tell us to do it; it just came naturally, and she started crying at that moment. She said, ‘That’s perfect.’ It was a special moment, and it was rewarding to be able to make her proud.”

Among the Bellas of fictional Barden University, Wilson is one of the most comical. On screen, that is.

“She’s really quiet and introspective off screen,” Regner says. “She has an innate sense of humor, and she’s one of the sweetest people I know. She’s also one of the smartest business people I know. I loved learning from her.”

And Kendrick?

“Her career has blossomed, and I’ve loved working with her,” Regner says. “She’s one of the most professional people I’ve worked with, and she has a career that I strive for — film, Broadway — she does it all. And yet she doesn’t take herself too seriously. We’re good friends.”

Returning to Baton Rouge for “Pitch Perfect 2” also was a reunion for Regner and her family and hometown. Once again, the Bellas were looking to her for answers to such questions as, “What is this place?” while filming the “riff-off” scene at Midnight Productions’ 13th Gate Haunted House.

“We were sitting there waiting to shoot, and there was a graveyard behind us,” Regner says, laughing. “I had to explain to them that this is a haunted house and how popular it is during Halloween.”

But there’s another aspect about her hometown and state that makes Regner particularly proud.

“Everyone I talk to loves filming in Louisiana,” she says. “They hear about the culture and the hospitality, and when they come to Louisiana, they find out it’s all true. I just hope the film industry in the state doesn’t go anywhere.”