On Thursday's American Idol, Keith Urban was brought to tears by Kelly Clarkson's heartbreaking performance of her song "Piece by Piece." After the show, the 48-year-old country crooner opened up about Clarkson's emotionally-charged appearance.

"[She's] just a phenomenal singer," Urban told ET. "She did a great job tonight."

Urban explained that he wasn't surprised by Clarkson's powerhouse performance because she's "so real," and addressed his tearful reaction to her poignant song, which she wrote about being abandoned by her father as a child.

WATCH: Kelly Clarkson Brings 'American Idol' Judges to Tears With Emotional Performance

"The song, it's insane. I figure you're either crying at this performance or you need to check your pulse," Urban said. "It's an amazing song."

Clarkson, who is pregnant with her second child and quickly nearing her due date, opened up about the song during the show, telling host Ryan Seacrest, "I actually wrote it pregnant with my little girl and now I'm pregnant with my little boy. So if I don't make it through and I start crying, just laugh. It'll make me feel better."

"I was starting to wonder if maybe I was [pregnant] too," Urban joked regarding his emotional, weeping response to hearing Clarkson sing.

"The humanity in that moment was just [incredible]," Urban continued in earnest. "You never see that, let alone on TV, so I was so grateful to be there to witness it."

WATCH: Keith Urban Honors His Late Dad: He 'Pointed Me in the Direction' of Country Music

As America Idol nears the end of its final season, it was important to find out what Urban planned on stealing from the Idol set, as a memento.

"I'm actually stealing Ryan Seacrest," Urban quipped. "He's gonna come and live with us and that'll be fun."

Check out Clarkson's awe-inspiring performance in the video below.

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