James Marsden Welcomes Baby Boy!

James Marsden on August 23, 2012 in Hollywood, California. Credit: Alberto E. Rodriguez/Getty Images

James Marsden is a proud papa once again.

The 39-year-old actor became a third-time father when Brazilian model Rose Costa gave birth to a baby boy, William Luca Costa-Marsden, on Friday, Dec. 14, in Los Angeles, a source confirms to Us Weekly.

Marsden -- already dad to son Jack, 11, and daughter Mary, 6, with ex-wife Lisa Linde -- dated Costa for a short time after his split with Linde, who filed for divorce in September 2011 after 11 years of marriage. Reports that the model was pregnant with the Straw Dog star's baby first surfaced in June.

Incidentally, the actor's character on 30 Rock is getting ready for fatherhood, too: He recently married Liz Lemon (played by Tina Fey) so the two could adopt a child together.