When January Jones welcomed her son Xander on September 13, she declined to reveal the identity of his father.
And on registering his birth the Mad Men star left his name off the certificate, reports US website TMZ.
Apparently Californian law stipulates that for the father's name to be included he would have to be married to the actress or be present to sign a statement of paternity.
January has previously been linked to Jason Sudekis, from Saturday Night Live.
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