"Camila gave birth to our third child yesterday morning. Our son, Livingston Alves McConaughey, was born at 7:43 a.m. on 12.28.12," he wrote on his Whosay page Saturday night.
"He greeted the world at 9 lbs., and 21 inches. Bless up and thank you for your well wishes."
Camila, 29, and her actor husband, 43, welcomed their third child in Austin, Texas, Friday, PEOPLE previously confirmed.
The couple – also parents to Vida, almost 3, and Levi, 4 – announced the pregnancy in July, just one month after they wed in Texas.