Kelly Clarkson brought Keith Urban to tears last week during her performance of "Piece by Piece" on American Idol. The pop-country superstar admits that she often has to hold back tears while performing the autobiographical song, which is about her relationship with her father.

"I don't even think I understood the gravity of [the song] until I was pregnant with River Rose," Clarkson tells On Air with Ryan Seacrest. "I was like, 'I cannot imagine not seeing this kid to his or her full potential and just seeing what she's going to do, what she's going to be like.' Why wouldn't you want to be a part of her life?"

While the response to the song has been incredible, the singer — who is expecting her second child soon — is sad that so many people can relate to the subject matter.

"I don't think I knew how much that affected me until writing that song," Clarkson reveals. "I definitely didn't know how it would affect me like it does when I sing it live because that's not fun."

Clarkson raves about her husband Brandon Blackstock being a "great father" and admits it's beautiful and difficult to watch his love for their daughter, as she grew up without having her father present in her life. However, she says she's moved on and isn't angry about his abandonment.

"I'm not angry about it anymore," she says. "I'm 33 years old, I'm a grown woman. But it's more of that thing where you can try your hardest to salvage relationships — and I did — but at the end of the day, if you keep getting hurt by someone because they just don't know how to properly love people, it's just not worth it."

Clarkson recently went into the studio to record the American Idol version of "Piece by Piece," which is now available for purchase. The new version will be added to Clarkson's Piece by Piece Deluxe Album, out March 4.

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