The "Who's the Boss" star, 38, and her husband, agent David Bugliari, welcomed a son Wednesday morning.
Milo Thomas Bugliari was born at 9:27am, Milano's reps tell TooFab. He weighed 7 pounds and was 19 inches long.
Alyssa wasted no time tweeting about the news, telling her followers "Thank you for all the well wishes for my son Milo. My heart has tripled in size. I love him more than all the leaves on all the trees."
Milo is the first child for the couple, who wed in 2009.
Milano, an avid Twitter user, shared many photos pregnancy online. Click on the "Launch Gallery" button to see all the photos: