The 39-year-old actress had been working with an agency for six months before adopting the newborn African-American girl, August, in July, according to the site.
Theron adopted her son Jackson from her native South Africa in 2012.
The adoption comes shortly after Theron abruptly ended her engagement to Sean Penn, whom she had been dating since 2013. However, earlier this week, the former couple was forced to reunite for re-shoots to finish the movie The Last Face.
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