Jamie Lynn Spears Felt 'Really Sad' When Justin Timberlake Dropped 'Cry Me a River'

On Monday, it was revealed Jamie Lynn will appear on Alex Cooper's Call Her Daddy podcast for a two-part episode debuting at midnight tonight. Ahead of the drop, PEOPLE got a preview in which Spears opens up about her sister's split from Justin Timberlake and how she, an early teen at the time, felt when it all went south.

"I think everyone thought it was forever. I was so sad, first off because my sister was so sad, but that, too, was the first time I saw [that] maybe I didn't know everything about the relationship," said Jamie Lynn. "Perhaps they were protecting me and obviously why would they talk to me about anything."

Britney and Justin dated for three years before they ultimately split in 2002. After their breakup, Justin released the music video for "Cry Me a River," a song about a cheating girlfriend. For years, Justin denied that his 2002 hit was written about Britney -- despite casting her lookalike in the video.

"I thought how heartbreaking it must have been for my sister when 'Cry Me a River' came out," Jamie Lynn continued on the podcast. "Don't get me wrong, like, that's a way to launch your solo career, right? That's a way to do it, but I felt really sad."

Britney would release the song "Everytime" in 2003, but has never publicly said the song was about Timberlake. The song's co-writer Annet Artani, however, said it was Britney's response to Justin's song. Jamie Lynn appears to confirm that account.

"And my sister, she wrote that song 'Everytime' and she's beyond brilliant with anything creative and she picked that song out on the piano and she wrote it and it still makes me cry because I think about how heartbroken she was, because that was her song and that was his song," she explained.

The Call Her Daddy podcast is just one of a select few interviews Jamie Lynn is doing to promote her new book, "Things I Should Have Said," a book which has sparked major drama between her and Britney. Over the past week, the two have gone back at forth at each other over claims Jamie Lynn makes in the book, as well as in interviews like "Nightline" promoting it.

Eventually, Britney said she does love her sister "unconditionally" and added that it's "so tacky for a family to fight publicly like this" -- while asking her sister to show her some loyalty, instead of showing it to "the people that hurt me the most" amid her conservatorship battle. Jamie Lynn responded asking for her sister to call her so they could settle it offline.

"I'm happy to share how many times I've reached out to you, supported you and tried to help you. This is embarrassing and has to stop. I love you," she added.

It seems she may share some of those messages on the Call Her Daddy podcast, as another clip from the show shows host Alex Cooper saying Jamie Lynn has a "text message that clears your name" ... before Spears reaches for her phone.