The proud dad reveals the media was so intent on getting information about the Legally Blonde star's newborn, they overlooked the fact that he and wife Megan Fox were in a nearby hospital delivery room ready to become parents.
In a radio chat with Los Angeles DJ Ryan Seacrest on Tuesday (06Nov12), the former Beverly Hills, 90210 star explained his son Noah Shannon was born hours after Witherspoon's baby on 27 September (12).
He said, "We got really lucky... We were lucky enough to go in at 2.30 in the morning to the hospital and nobody knew. We were there for two days... and we heard Reese was at her place and had a baby, and we got out of the hospital and nobody knew (about us).
"We got home and thought, 'This is unbelievable', because we weren't expecting to get away with it."
Fox eventually released the baby news via a post on her Facebook.com page two weeks later, writing, "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."
Green adds, "I've been wanting to send Reese Witherspoon flowers for, like, a month and a half... Reese, your ice cream cake is on the way."