What makes Keith Urban cry? Kelly Clarkson, apparently. The original American Idol winner had Urban and plenty of others in the Idol audience in tears following her performance on the show on Thursday night (Feb. 25).

Clarkson, who served as a guest judge during the two-hour episode, stunned with her performance of the emotional song. Accompanied only by a piano, the singer herself even hard trouble getting through the tune, about how her husband, Brandon Blackstock, has become the father to their daughter (and soon-arriving son) that Clarkson's own dad wasn't. She earned a standing ovation from the judges and the crowd, who chanted "Kelly! Kelly! Kelly!" as Clarkson ended her performance.

"This is very memorable, me crying," Clarkson joked after she finished singing. "Piece By Piece" has left the artist in tears before -- most notably, at a show in August, when she revealed that she was pregnant again after becoming emotional during the tune.

“... I hate this song right now,” she told the crowd that night. “My makeup artist is backstage hating me right now. I just don’t want you to think I’m on pills or drunk."

Press play on the video above to watch Clarkson's Idol performance. Her second child is due any day.

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