Which Ex Will Taylor Swift Sing About at the CMA Awards?

Credit: Bryan Bedder/WireImage for Vogue

Taylor Lautner will make an appearance the Country Music Association Awards in Nashville on Wednesday...via song, that is.

His ex, Taylor Swift, is set to sing about the 18-year-old Twilight star when she performs her latest single, "Back to December," UsMagazine.com can exclusively confirm.

In the track, Swift, 20, sings that she wishes "I'd realized what I had when you were mine. I go back to December, turn around and make it all right."

"She rehearsed last night and sounded great. It's a very emotional performance -- just her sitting at the piano, strings playing," a source tells Us. "It'll definitely be a 'moment' in the show."

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Hopefully Swift's current beau Jake Gyllenhaal remembers to set his TiVo: an insider tells Us that the actor, 29, hasn't attended rehearsals and probably "won't be here for the CMAs."

The Country Music Association Awards air Nov. 10 at 8 p.m. (EST) on ABC.