Her husband John retweeted the message on his own account.
Chrissy and John have not revealed the name of their bundle of joy, so we'll have to wait for it!
The couple are also parents to two-year-old daughter Luna Simone.
It's not clear exactly when Baby Boy Legend made his debut as Chrissy's Instagram shows her taking a bath with baby Luna just yesterday.More news: See the Xbox Adaptive Controller in Action
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The little boy joins his sister, Luna, 2.
Before adding: "Wanna hold my boy let's do thisssssss'".
Meanwhile, the "All of Me" singer told ET last month, "It's always exciting, because you never know what they're going to be like". I think she'll probably have some growing pains because she's currently running the house right now.
Chrissy herself had shared in an interview that John's only available embryo is that of a male child so yeah she is definitely having a boy. "I don't know if she's ready for that yet".
She faced huge criticism for this reveal and was forced to defend the couple's decision to have a child via IVF.
Chrissy and John have been together since 2007 and were married in 2013.