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Keith Urban loves that his two daughters have such different personalities.

The "American Idol" judge, 45, said he and wife Nicole Kidman's oldest child, Sunday, 5, is truly the light of their life.

"She's really aptly named, 'cause her nickname's Sunny, of course. And she's just so sunny," he told ABC News Radio. "It was incredible. She's really her name. Her disposition is very up and sunny."

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While Sunday is Urban's upbeat daughter, the doting father says his 2-year-old Faith Margaret is more of an introvert.

"She has a different kind of inner, inward kind of thought-energy thing," he said. "Even at two-and-a-half, you can see it. So, it's going to be interesting to see how they keep blossoming."

The Grammy Award winner is used to writing and singing country ballads when he's not molding young talent on "Idol," but said his two little girls force him to play a different kind of music at home.

"There's a Scottish program called 'Shaun the Sheep,'" he said. "And they love this 'Shaun the Sheep,' and there's this crazy theme … that they always have me play on the piano. I had to learn it. So, I play 'Shaun the Sheep,' like, all the time."

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Hopefully "Shaun the Sheep" didn't have too much influence on his latest album, "Fuse," which Urban told ABC News in August was inspired by Kidman and the couple's two daughters.

"They inspire so much of what I do," Urban said. "They hear everything. Nic is hearing all the songs as they're coming in and she lives with this record as long as I do."