The former The O.C. star only confirmed her pregnancy via Twitter.com in October (12) and it appears she has already welcomed her first child, who she has named Calin, according to UsMagazine.com.
Taking to her Facebook.com page on Sunday (16Dec12), Armstrong writes, ""Thank you so much for all the love! Will post pictures after a little rest. We're all doing wonderfully. It was an amazing experience and we couldn't be more thrilled with our new arrival.""
The identity of the tot's father has not yet been revealed.