January Jones welcomed a baby boy on Tuesday, People reports.
Jones, 33, and son Xander Dane Jones are "doing great," her rep tells the magazine.
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The Emmy-nominated actress chose not to find out the sex of the baby during her pregnancy. Jones, who announced she was expecting in April, has not publicly commented on who the father is.
Jones will reprise her Emmy-nominated role as Betty Draper when Mad Men returns for Season 5 next spring. She was most recently seen in X-Men: First Class.