Ambrosio announced the news on Facebook last night, posting a photo of herself on the beach with her hand on her baby bump.
"Because I already have a daughter I know what to expect with a girl, so having a boy means it's going to be surprising all over again," Ambrosio wrote. "My fiancé is so excited. Now he has company! He won't be in a house full of girls anymore!"
Sims, who like Ambrosio has walked in the Victoria's Secret Fashion Show, told the world about her happy news on Tuesday's episode of The Talk. "The only reason why I'm telling this is because we can't make a decision on the nursery," she said. "We are having a baby boy!"