January Jones and her son Xander Credit: Brooks/INFphoto.com

January Jones is a tough nut to crack. When The New York Times asked the Mad Men star to reveal who fathered her 20-month-old son Xander, the 35-year-old actress refused to answer. "That's my son's business," Jones explained in a May 19 interview. "It's not the public's business."

Though she's often asked to divulge details, Jones prefers to keep family matters private. "Jack Nicholson once told me: 'You should never give your personal life away, otherwise people will pick you apart. They'll never believe in your character,'" she quoted the notoriously tight-lipped actor as saying.

"Women should have lots of secrets," added Jones, whose famous exes include Jason Sudeikis, Ashton Kutcher and Josh Groban. "It's our right to have secrets. Otherwise, what would we write in our memoirs?"

Jones was slightly more forthcoming when discussing her son's mini-milestones. "His first word was 'Mama,'" she said of Xander. "His second was 'back,' cause I kept saying, 'Put it back.'"

In regards to eating her placenta after Xander's September 2011 birth, Jones told The New York Times, "It was like taking a vitamin blended into a smoothie. I'm a mammal. I nursed. I did all kinds of weird stuff."

Mad Men airs Sundays at 10 p.m. EST on AMC.