The actress stepped into the recording booth at Dolly Parton's request, to sing "Push and Pull" with her co-star Danielle Macdonald, and as she told ET, it ushered out the waterworks.
"[I was so nervous] but I sang through it and then got my voice. I literally couldn't have a squeak come out, and then when we finished, I remembered, I just burst into tears," Aniston told ET's Nischelle Turner at the Dumplin' junket at the Four Seasons Beverly Hills on Tuesday.
"She did get emotional after she was done," Parton -- who crafted the soundtrack -- confirmed, calling the actress a "real pro" in the booth.
"It was terrifying and fun and all of it... it was great," Aniston recalled. "[I was] fearless, yes, or fearful, depending on how you look at it. But I had Dolly and Linda Perry there, who were just patient and wonderful."
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'Dumplin'' First Look: Dolly Parton on Working (and Singing!) With Jennifer Aniston
The 49-year-old actress said the experience brought back childhood memories of singing into hairbrushes and wanting to be a rock star. "I sort of had this weird dream of a lifetime just come crashing in on me," she said. "But boy... bow to all of those guys who do that. It's quite fab. It's fantastic."
Dumplin' stars Aniston as a former beauty queen whose plus-size teenage daughter, nicknamed "Dumplin'" (Macdonald), signs up for her mom's pageant in protest. The role required the former Friends star to speak in a southern accent -- and it got a big stamp of approval from Parton.
"I love picking up on accents anyway. It's something I've always been able to do a little, and that one in particular. But I also have a fantastic dialect coach who just sort of would give me little tips here and there," Aniston explained. "[The toughest thing] is not knowing if you got it right."
"I thought she did great, and I told her that. I went to see it with her... I was really impressed and I knew she worried about it," Parton recalled. "She needed to hear it from somebody who knew, so I leaned in and said, 'Your accent is great, you did a great job,' and she said, 'Whew!' but I meant it."
Stepping into the shoes of a beauty queen came a little easier.
"Especially if you're doing award shows, it's very much like what she's talking about -- the dresses and the beauty pageants, don't you think?" Parton asked Aniston. " It's kind of similar."
"It's a performance," Aniston agreed. "[It's] a little bit of going out there and putting on your sparkly, pretty self."
Dumplin' launches on Netflix and in select theaters on Friday.