Freaks and Geeks star (and recently engagedLinda Cardellini was one of Mad Men's most surprising guest stars ever, and apparently with good reason—upon being cast in the series as the Drapers' neighbor and Don's mistress, Sylvia Rosen, she was sworn to secrecy until her first episode premiered. In a new interview with the New York Times, Cardellini detailed the lengths she had to go to keep the role under wraps:

Q. Has the gag order been lifted? Are you allowed to go outside your house?

A. The house arrest is lightening up [laughs]. Nobody really knew that I was doing this. It’s rare that you can keep that kind of a secret, especially from people within the industry. It’s been fun to see friends who I’ve acted with over the years find out that I’m on the show. [...]

Q. You couldn’t really tell people that you were playing this character, or even that you were on “Mad Men.”

A. No. I couldn’t even tell people I was working [laughs]. But after having a new baby, people weren’t really asking that much anyway. I had taken some time off because I had worked nonstop since I was young, and I hadn’t really taken any time off. I did this one film, “Return,” and traveled around with that some. We went to Cannes with the film, and I think that’s where my daughter was conceived [laughs]. Then I had the baby and took even more time off. So coming back to TV has been really fun, and being able to do it in a way that has, fortunately, surprised people.

Cardellini also divulged a little about the process she went through to get cast—basically, she was told nothing about Sylvia's characterand commented that, "to be the woman who can bring Don Draper to his knees is nothing short of fun." She also said that creator Matthew Weiner does have a single vision for Don's character arc. "Don’s arc is so deeply structured—Matt always has a master plan but the details are being worked out," she explained. Sadly, there was no mention of those crazy Mad Men theories that have been floating around lately.

You can check out more from the interview here.

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[via NY Times]