Fans were left wondering who the baby's father is, after she showed off her bump yesterday.
Taking it into her stride, the 29-year-old shared a photo of her three past co-stars — Shia LaBeouf, Will Arnett and Jake Johnson — along with the hashtag “#notthefather”.
Despite the fact that the mum-of-two is estranged from her husband, Brian Green Austin, People confirm he is the dad.
"Of course Brian is the dad! They never stopped loving each other and they will never stop being devoted parents to their boys,” a source close to the pair revealed.
The pregnancy came as a surprise for the couple who are "very excited" and are "continuing to work on their marriage and are living together again," another insider quipped.
The couple are already parents to Noah, three and two-year-old Bodhi.
"They both love being parents," a close pal admitted about the duo.
Megan filed for divorce in August after five years of marriage and 11 years together.
The Teenage Mutant Ninja Turtles leading lady and the 42-year-old have remained amicable since announcing their split.
The former couple stepped out together in Santa Monica, less than one day after the she revealed she was expecting. Onlookers noticed they appeared to “be in good spirits”.
Megan and Brian have yet to officially comment on their exciting news.