Carrie Underwood has shared the song she wrote about her son Isaiah and husband Mike Fisher. "What I Never Knew I Always Wanted" is the last track on Storyteller, and by far her most personal.

"It's a love song for my boys," Underwood tells Taste of Country, admitting that she doesn't think she'll be able to perform the song live. Her longtime fans know there's a song like this on every album, but still she was hesitant to include it.

"Enough people were like 'This has to be on the album,'" the 32-year-old adds.

That makes four songs revealed from Storyteller, Underwood's fifth studio album. "Smoke Break" is the current single, but the singer made "Heartbeat" and "Renegade Runaway" available to fans who pre-order the album, and put them YouTube. Mark Bright returns to co-produce the album, while Jay Joyce worked with Underwood for the very first time.

"What I Never Knew I Always Wanted" was co-written by Brett James and Hillary Lindsay and it's the only mommy moment on the album. Many of the songs were discovered or written prior to her becoming pregnant with her first child.

This one was penned after she became a mother, obviously. It was a struggle to return to work, Underwood says, admitting that "Mommy guilt is so real." She'd start slowly, writing just two days a week in a cabin that's near a vacation cabin on her property. Baby Isaiah would be in that other cabin, yet she still felt she was missing something.

“Sometimes I just sit there and I’m like, ‘I’m kind of sorry that this is your life, traveling around," she explains in the video below. "I’m sure you’d just rather be home in your space. And you’re in this hotel room in Lord knows where. Or you’re on a bus.’”

Storyteller drops on Oct. 23.

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