LISTEN: another new song from Taylor Swift's vault!

Taylor Swift just brought some new life to a blast from the past -- by recruiting pal Jack Antonoff to help rework "Mr. Perfectly Fine," the latest teaser from Fearless (Taylor's Version).

The song was recorded during the 2008 sessions for Fearless, but never released. It's one of Tay's trademark breakup songs, with lines like “Hello, Mr. perfectly fine/ How’s your heart after breaking mine?/ Mr. always at the right place at the right time/ Baby. Hello/ Mr. casually cruel/ Mr. everything revolves around you."

She hinted on social media that the song was autobiographical, saying, “Me in 2020: Life is chill, writing songs based in fiction to avoid drama, feeling pretty grown up. My 2008 music from the vault, in a goblin voice: REELEEEEEEEASE MR. PERFECTLY FIIIIIIIIINE.”

Some think that the song might be about Joe Jonas, who dumped Taylor shortly before she recorded Fearless.