"It's 6:10 am. I have barely slept and I am with the two best men in the world. My son and my husband," Williamson posted on Twitter. "I am the luckiest."
McGreggor Edward Roberts was born on September 21. The little one weighed in at 7 pounds, 4 ounces.
Williamson, who received her second consecutive Outstanding Supporting Actress Daytime Emmy nomination earlier this year, joined the cast of the ABC soap in February 2003.
Photo: Kat Guarino/Soap Central