Actress-filmmaker Jennifer Siebel Newsom and her husband, San Francisco Mayor Gavin Newsom, welcomed the arrival of their first child today.

Weighing in at a healthy 7 lbs. 12 oz. and 20.5 inches, Montana Tessa Siebel Newsom was born at 12:39 p.m.

Their daughter is named after the state where the couple's July 2008 wedding was held on the grounds of the Siebel family's Bitteroot Valley ranch. Her middle name honors the Mayor's late mother, Tessa Newsom, who died of breast cancer in 2002.

Not surprisingly, the "revolution" was Twitter-ized by the proud, but nervous, papa to his more than one million "followers."

Much happiness and best wishes to Mrs. Newsom, Mayor Newsom and their families!

P.S.: A happy Tweet from Daddy Newsom.

P.P.S.: "Jen doing great," tweets Dad. Then realizes it's time for Dad to step away from the Twitter.