The 39-year-old artist and her boyfriend, Jason Bleick, named their son Arthur Saint Bleick, according to People magazine. The baby weighed in at 7 pounds and 12 ounces.
Blair and Bleick, a fashion designer, met while the two were collaborating on his EVER fashion line. Blairannounced her pregnancy back in January.
Blair played Liz in the 2004 film "Hellboy" and its 2008 sequel and was seduced by Sarah Michelle Gellar's manipulative school queen character in the 1999 movie "Cruel Intentions." Blair is currently filming the movie "Dark Horse" with Christopher Walken and Donna Murphy.