The couple started dating in 2004 after meeting on the set of Hope and Faith — at the time Megan was 18, and Brian, 30.
They originally got engaged in 2006, but called it off in 2009 before reuniting in 2010.
In June of that same year, they were married in a romantic, private ceremony in Hawaii. Noah was born on 27 September, 2012.
They managed to keep the little boy's arrival a secret for two weeks, before Megan confirmed the rumours on her Facebook page.
"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 boundless, immaculate love," she said.
"Thanks to those of you who wish to send your positive energy and well-wishes."
She has since spoken of her desire to give Noah a sibling. "All I wanted to do my whole, whole life was have a baby and, now, I've finally done it," she told Marie Claire earlier this year.
"I just want to give Noah as much of myself as I can. And I want to have more kids. That is where my heart is."
Megan is currently in New York filming as reporter April O'Neill in a new big screen version of Teenage Mutant Ninja Turtles. Just a few days ago, she was pictured on set, her tummy covered up in a loose vest top.