Katharine McPhee poses in stepdaughter Sara Foster’s swim line one month after giving birth: ‘You nail it’

Former "American Idol" standout Katharine McPhee showed off her newly-acquired post-baby curves in a selfie snap shared to her Instagram Story on April 1 as she modeled a one-piece tie-dye swimsuit created by her stepdaughter, Sara Foster, 40.

The singer-songwriter, 37, who welcomed her first child, son Rennie David, with husband David Foster, in late February, showed off her newly-acquired curves in a selfie snap shared to her Instagram Story on April 1 as she modeled a one-piece tie-dye swimsuit created by her stepdaughter, Sara Foster, 40. "Best one-piece I’ve ever tried," the "American Idol" alum began in a caption for the image. "Usually it’s cut too low and the torso isn’t long enough. Straps are adjustable. So comfortable. You nail it @sarafoster." Earlier in the week, the Broadway star also posed in a one-shoulder, two-piece bikini and embraced her post-baby figure in the process.