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Nicole Richie has decided to undergo cosmetic surgery to increase the size of her breasts, according to Us Weekly.

The mother of Harlow, 3, and Sparrow, 2, has been hitting the gym lately with a noticibly larger chest.

A source, who says the Fashion Star mentor got implants over the summer, tells the mag, "In the past, she said she wanted a lift, though we never thought she was serious."

The House of Harlow 1960 designer, 30, wanted to "improve her bustline," the source says, adding, "The pregnancies took a toll. She said breastfeeding killed what boobs she did have!"

Nicole's hubby Joel Madden, 32, is probably not complaining.