James Marsden has welcomed his third child.

The X-Men star's ex-girlfriend Rose Costa delivered a son on Friday (December 14) in Los Angeles, People reports.

Marsden and the Brazilian model dated briefly following his divorce from wife Lisa Linde in 2011.

A source revealed that the actor chose the name of their new son, William Luca Costa-Marsden, and is being very supportive.

Marsden is already father to 7-year-old daughter Mary James and 11-year-old son Jack Holden with ex-wife Linde.

He currently stars in 30 Rock as Tina Fey's love interest, and is also set to appear in the upcoming comedy Walk of Shame.