After surviving breast cancer, Christina Applegate opens up in this week's issue of PEOPLE magazine with an exclusive photo shoot and interview about her role as a new mom to her 7 lbs., 8 oz. baby girl Sadie Grace, who has brought her a newfound sense of healing, hope and love.

Self-conscious about her chest since being diagnosed with breast cancer in 2008 and opting for a double mastectomy, Applegate had kept her hospital gown securely fastened even as she neared her 18th hour of labor on January 27th. "I don't let anyone see my top half," says the actress, who has undergone reconstructive surgery. "That whole area has remained very private."

But that all changed the moment an exhausted Applegate, 39, gave one final push and watched as her daughter Sadie Grace was born. Without hesitation, she let her gown fall off as the nurses placed her baby on her exposed chest. "It was such a liberating and beautiful moment," she tells PEOPLE. "I didn't care. It didn't matter anymore. Not only was she the most beautiful thing that's ever happened to me - but she saved me too. I got to abandon resentments that I've held on to in that vicinity for years because [my chest] is where she feels the most comfortable and where she's the happiest."

Applegate has found her own realm of newfound bliss with musician-fiancé Martyn LeNoble, 41, less than three years after the toughest battle of her life. Holding her 2-week-old daughter, with LeNoble's arms around them both, the actress is utterly overwhelmed by the sense of love she feels for Sadie. "It's just a miracle, and you can't explain it," she says. "She's healed me in so many ways…I've been kind of sad for a long time, and she's just opened up my whole soul."

The couple, who got engaged last year on Valentine's Day, were ready to start a family but still surprised to find out Applegate was expecting. "We were actively not not trying," she says, smiling. Her cancer history wasn't an obstacle to conceiving - "I didn't have chemo or radiation, so I didn't have to worry about that," she says - but the pregnancy still posed some risk. Because Applegate is a carrier of a gene that increases the risk of developing breast and ovarian cancer, her remission could have been affected by her pregnancy hormones. The star, who is routinely screened for any recurrence, says she decided to leave the fretting to her doctors. "I knew they'd stay on top of it," she tells PEOPLE. Still, she admits, "no one told me it would be a problem, which was good, because if you plant that seed in my head, that's not a good thing. Ignorance is bliss."

These days, Applegate is still weary of the "c-word." Nevertheless, she discovered that several of her nurses in the maternity ward were unaware of her health history. Says LeNoble, "It was in our birth plan: Don't inform us about breast-feeding, because it's not going to happen." Instead, says Applegate, "You don't know how many times they asked me, 'So, are you going to breast-feed?'" Her response? "I tried not to freak them out and just say, 'No, I've chosen not to.'"

By her side throughout this entire journey has been LeNoble, who she's known for more than 14 years and dated since 2008. "He's my best friend. And now watching him with our daughter, I have fallen even more in love," says Applegate, who is keeping their wedding plans a secret. Adds LeNoble: "It's all been amazing and perfect."

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