January Jones Leaves Baby Daddy's Name Off Birth Certificate

Mum's the word!

After welcoming son Xander Dane on Sept. 13, January Jones still has yet to reveal the identity of the child's father. According to documents filed Friday with the Los Angeles County Department of Public Health, the "Mad Men" star, 33, even went so far as to leave the father's name off her baby's birth certificate.

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Although the "X-Men" actress -- who dated "Saturday Night Live" actor Jason Sudeikis, singer Josh Groban and Ashton Kutcher in the past -- has not been spotted out with her bundle of joy, her fellow "Mad Men" crew is bubbling with excitement for the new mommy.

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"We're all so proud of her and happy for her, and she's doing really well," co-star Elizabeth Moss recently told Us Weekly.

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On Sunday, "Mad Men" costar John Slattery gushed about the blond bombshell's babe. "I've seen a picture of the baby. He's beautiful," Slattery told Us at the Rape Treatment Center's Annual Brunch. "She's in love with that boy."

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Check out photos of January's baby bump