Green and wife Megan Fox welcomed Noah Shannon into the world on September 27. They managed to keep the news quiet for almost a month as the paparazzi was busy covering the birth of Witherspoon's son Tennessee at that time, the Daily Mail reported.
"We got really lucky. And I've been wanting to send Reese Witherspoon flowers for, like, a month and a half. 'Cause she actually gave birth, I think the day before us in Santa Monica, " Green told Ryan Seacrest.
"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. We got home and thought, 'This is unbelievable. Because we weren't expecting to get away with it. So we just figured we would go with it as long as we could," Green added.
The 39-year-old actor already has a son Kassius, 10, from a previous relationship but it is first child for Fox, 26.