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Kelly Clarkson debuted a hot, new figure with the premiere of her show Duets last week and the singer is crediting her recently slimmed bod to boyfriend, Brandon Blackstock.

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"No one wants to be untoned when you're dating someone," the 30-year-old singer tells Life & Style of her motivation to get fit and trim. "I've always fluctuated, but now I'm in a happy relationship."

While Clarkson reveals her beau (who is stepson to country legend Reba McEntire) helps her stay "more active" these days, she says the two will never, ever work out together.

VIDEO: Behind-the-Scenes with Kelly Clarkson

"We did that once," she admits. "I don't like huffin' and puffin' in front of my man and looking all red and gross and sweaty"