The actress, who has appeared "Cruel Intentions," "Legally Blonde," and the "Hellboy" franchise, gave birth on Monday. It's the first child for Blair and her boyfriend, Jason Bleick, whom she met while collaborating on Bleick's EVER fashion line.
They named their son Arthur Saint Bleick. People was the first to report the news.
Blair remained very active until her due date, and was spotted all over Hollywood sporting a giant baby bump. Click on the "Launch Gallery" button below for all her maternity photos:
Blair was formerly married to rocker Ahmet Zappa (son of Frank) from 2004-2006.