What a difference a baby makes! That’s what stars of Grey’s Anatomy are saying about their co-worker Katherine Heigl. A source tells BettyConfidential that Katherine has become a changed woman since she and her husband, singer Josh Kelley, adopted their daughter, Naleigh, a special-needs child from South Korea last fall.

“She's mellowed out since bringing home Naleigh,” says the source. “She’s a doting mom. She doesn’t like to be apart from her baby, so she brings her to the set as often as she can.” And co-stars are not complaining! “Katherine loves showing off Naleigh. And her co-stars get a kick out of her,” says the insider. “She’s such a good baby. She’s always smiling and hardly ever cries.”

As BettyConfidential previously reported, Katherine (who returns to TV screens tonight as Dr. Izzie Stevens) had been labeled a diva on the set. “She’s really trying hard to be pleasant and not offend anyone this year,” adds the source. “She’s by no means anyone’s best friend, but she’s tolerable and that’s the main thing. Everyone is more at ease with less tension on the set.”

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 When Katherine joined Grey’s Anatomy in 2005, she and her now ex co-star, TR Knight, became fast friends, but it seemed the pair courted drama. Katherine complained loudly and publicly about her long working hours and TR had a much-publicized feud with Isaiah Washington. Last season, when TR left the show, everyone thought Katherine would be easier to work with, but that wasn’t the case.

“She and TR hung out together on the set all the time. Once he was gone, everyone thought she’d be friendlier. But she started rattling the cages again, complaining about scripts.”