"Brooke and I are thrilled!" Sheen says in a statement released Monday.
"She's the best stepmom Sam, Lola and Cassandra could ever hope for. Seeing her love and affection with those three, I know she'll be an amazing mom. Unless I bat 100 percent, perhaps a boy awaits us."
The Two and a Half Men star already has three girls. Sam, 4, and Lola, 3, are his daughters with ex-wife Denise Richards, and Cassaundra, 23, has ex-girlfriend Paula Profitt as a mom.
A family source tells People, "Brooke found out for sure on Friday and is thrilled to death. Brooke loves Charlie very much and has wanted a baby for some time."
The couple married in May in front of 60 close friends and family, and began talking about kids soon after the wedding.
"Hopefully triplets!" says Mueller, 30. "Could you imagine if I really had triplets? He'd be like, 'Whoa!'"
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