The 39-year-old musician added his vocals to 'Exile' on the megastar's 2020 album, 'folklore', and also co-wrote the title track and played on several other tunes on the record.
And this week, he teased a snippet of another song with the 'Shake It Off' hitmaker.
During an Instagram Live, he said: “That’s the awesome Taylor one. I think this should be the single."
It's not known if the acoustic song is intended for Justin's side band Big Red Machine with The National's Aaron Dessner - who also worked on 'folklore' and its sister record, 'evermore'.
Big Red Machine released their self-titled debut LP in 2018.
Taylor, meanwhile, has just released the first of her re-recorded albums, 'Fearless (Taylor’s Version)'.
The 31-year-old singer's new version of the 2008 Grammy-winning LP features 26 songs and six previously unheard tracks.
Taylor had already released ‘You All Over Me (From the Vault)’ featuring Maren Morris, 'Love Story (Taylor's Version)' and 'Mr. Perfectly Fine (From the Vault)'.
The latter was penned in 2008 but never made it onto the final track-listing for the original cut of 'Fearless'.
Keith Urban - who the 'cardigan' hitmaker supported on the 'Escape Together World' in 2009 - duets with Taylor on 'That's When' (From the Vault)' and the Australian superstar also added harmonies to 'We Were Happy (From the Vault)'.
'Bye Bye Baby' concludes the six unreleased cuts from 'Fearless'.
The final song on the track-listing is the bonus remix 'Love Story (Taylor's Version)' by Elvira Anderfjärd, a Swedish producer who has worked with the likes of Katy Perry and Tove Lo.
Taylor had previously revealed her plans to release new versions of her first six records after her arch-nemesis Scooter Braun's Ithaca Holdings bought the rights to the master recordings
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