"Sarah Michelle and Freddie Prinze Jr. are thrilled to announce that they welcomed a baby son into the world this past week," her representative told UsMagazine.com Monday.
"Mother and baby are doing great and Charlotte is very excited to be a big sister."
No other details regarding the baby's birth were immediately available.
Gellar and Prinze Jr. met on the set of the 1997 movie "I Know What You Did Last Summer" and married in 2002. They are also the parents of 3-year-old Charlotte Grace.