|Brian Austin Green and Megan Fox|
A source told America's Star magazine: "They just found out and are incredibly excited."
Megan and Brian had kept the news to just close family and friends something they have found difficult because they are so excited about the baby.
The source added: "It's still early, so they are only telling close friends and family members."
The 'Friends with Kids' star has already had lots of parenting practise as she is stepmother to Brian's nine-year-old son Kassius, his child with actress Vanessa Marcil.
The source said: "Megan has become a great stepmom, and Brian knows she'll be wonderful with the baby. She has really grown in the past couple of years ... her family comes first."