The `Transformers` actress and her husband Brian Austin Green became parents last month, but have waited until 17.10.12 to reveal their first son together to the world.
Megan wrote on her Facebook page: "We have been very lucky to have had a peaceful few weeks at home, but I would like to release this myself before others do. I gave birth to our son NoahShannonGreen on September 27th. He is healthy, happy, and perfect."
She went on to thank God for a healthy baby and well wishers for their support.
She wrote: "We are humbled to have the opportunity to call ourselves the parents of this beautiful soul and I am forever grateful to God for allowing me to know this kind of boundless, immaculate love.
"Thanks to those of you who wish to send your positive energy and well wishes. May God bless you and your families abundantly."
Many rushed to wish the couple well and post their congratulations.
Donise Patterson wrote: "Congrats, I have a son namedNoah and a Brother namedShannon, good names." Consultant Dana Tosta wrote: "Wow Megan this is so sweet & sacred... a time of deep interconnectedness for you and the baby and an even deeper connection to your husband(sic). "I always suggest finding a good Kundalini yoga class. You have the best kundalini center in LA (sic)!" Megan is also stepmother to Brian`s son Kassius, 10, from a previous relationship.