Carrie Underwood tells ABC's Nightline that her new album contains a song that's so emotional for her that she'll never perform it in public.

The album, Blown Away, comes out May 1, and it includes a song called "Forever Changed," about a married mom who is dying.

One of the song's writers said he wrote it about his mom, who had Alzheimer's. For Carrie, it reminds her of her grandmother's death.

“I get emotional even talking about this song, to be honest. It’s just beautiful,” Carrie said with tears in her eyes.

Carrie says she remembers her grandmother getting confused.

“It just becomes very real. . . . and I remember my grandmother at the end of her life, looking at my dad and thinking that that was my grandfather.”

Concertgoers likely won't ever hear the song performed live.

“I can never sing this song, like onstage in front of people," said Carrie. "I could barely get through it in the studio."