Brandi Carlile says she was dreaming big when she sent a handwritten letter to Dolly Parton with a special request. But in that note, Carlile said something she can never take back.

Carlile asked Parton if she would be interested in covering the title track of her 2007 debut The Story for a new benefit album supporting children impacted by war.

Her only mistake was suggesting that they drop the song's key down in case it was too high for Parton's vocal range.

"I'm sharing with you my humiliation because it's making me feel better every time I say this," Carlile recalled Tuesday (April 25) during her concert at Nashville's Ryman Auditorium. "You may have noticed, there's a couple high notes in that song. So I write in the letter, 'And don't worry, Dolly, I'd be happy to drop it down a couple of keys for you.'"

Parton's response is worthy of framing. In a beautiful letter on high-end paper with the official "Dolly" letterhead, the music icon said she would be honored to sing the song.

"It just says 'Dolly' on top of it in about three-inch letters in hot pink, and then the 'y' becomes a butterfly," Carlile described onstage. "So she writes back in the letter and she goes, 'And honey, don't you worry about changing that key. I'm going to Dolly-ize it. I don't expect to do it justice like you, but I promise you, that key will be fine for me.'

"When you listen to Dolly sing 'The Story,'" Carlile continued, "you'll notice, every note I hit, she starts there and then goes above it. I felt my life flashing before my eyes."

Carlile's set at the Ryman included The Story in its entirety, Led Zeppelin's "Going to California," a few song requests from fans and new tracks from a follow-up to 2015's The Firewatcher's Daughter.

Cover Stories: Brandi Carlile Celebrates Ten Years of The Story -- An Album to Benefit War Child lands May 5. Kris Kristofferson, Margo Price, the Avett Brothers and Adele are among the country, Americana, rock and pop acts who've contributed performances for the 14-song compilation.