Credit: Jim Spellman/WireImage.com; Nicolerichie.celebuzz.com

On Friday, Nicole Richie took to her Twitter page to announce that she and beau Joel Madden have welcomed a "new addition" to their "growing family": Tabitha Jones Madden, a cat.

Richie, 28, writes on her website that she found Tabitha crying outside her home "one dark and lonely night."

"At first, I thought it was Joel," says Richie, mother to daughter Harlow, 2, and son Sparrow (who turns 1 next month). "But to my surprise, there she was. A sad, and very hungry kitten."

Initially, she thought the cat belonged to her neighbor, so she ignored it.

A week later, the cat returned. "She was so skinny and I could tell she was starving," Richie writes. "I couldn't resist. I fed her, and she was as happy as Benji Madden in a sorority house. It's been 2 months now, so I think it’s safe to call her mine."