Los Angeles, California - Taylor Swift is joining forces with Eras Tour opener Gracie Abrams for a surprise feature on the 24-year-old's upcoming album, The Secret of Us.

On Monday, Gracie unveiled the complete tracklist for her anticipated sophomore album, which drops on June 21.

Naturally, the announcement sparked a total fan frenzy with the reveal that the 34-year-old pop star will be featured on the fifth track, titled us.

Gracie later shared her excitement over Taylor's involvement with a special message shared on her story.

Taylor Swift Taylor Swift leaves Stevie Nicks in tears with emotional Eras Tour tribute

"all i can tell you for now is that some of the most fun i've ever had in my whole life was writing this song together," she wrote. "i am currently smiling and sweating thinking about it and i'll never get over the shock of seeing this one on the tracklist."

The Risk singer was the most frequent supporting act on The Eras Tour in North America last year, and she's due to join the concert series again this fall when Taylor travels to Miami, New Orleans, Indianapolis, and Toronto.

While us. will mark the pair's first official collaboration, Gracie joined the Karma artist on stage for a special duet at The Eras Tour in Cincinnati, Ohio, last July.

When inclement weather delayed the show – thus cutting out Gracie's opening set – Taylor welcomed her on stage during the acoustic set to play I miss you, I'm sorry from Gracie's debut EP, Minor.

After the announcement of the duo's new collaboration, eagle-eyed Swifties noted that Taylor appeared to tease the track in the music video for Fortnight.

The video for The Tortured Poets Department's lead single featured a shot of the Cruel Summer songstress reading a book with "Us" written on the back cover, and the same book was included in one of the pop-up events in Los Angeles before the album's release.