Carrie Underwood and Reba McEntire are teaming up in the recording studio for an upcoming project, but fans will have to wait to see what they have in store.

The country music superstars have been working together at the Cash Cabin recording studio outside of Nashville. Musician and noted producer John Carter Cash posted to Instagram on Wednesday (Nov. 4), sharing two pictures of Underwood and McEntire from inside the studio.

The first picture shows McEntire appearing to arrive at the session, wearing a mask and carrying a water bottle as a smiling Underwood sits on the sofa and contemplates her phone.

A second shot shows McEntire seated and seemingly listening intently.

Cash — who is the only child of Johnny Cash and June Carter Cash — accompanied his post by tagging both artists and the studio, including the hashtag #secretproject. He shared no further details.

Johnny Cash built Cash Cabin as a refuge in 1979, according to the studio's website. The cabin has hosted all manner of music stars from across genres over the years, and it was gradually converted into a top-flight recording space. Johnny Cash recorded much of the bulk of his later-period American Recordings there, and John Carter Cash has produced a wide array of well-respected projects at Cash Cabin, including sessions from Loretta Lynn and Billy Joe Shaver.

Neither Underwood nor McEntire has posted publicly about whatever project they've been working on together.

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