Afshin-Jam, a human rights activist, made the announcement this morning on Twitter.
"Love my boys but looking forward to having another female voice in our house this fall. A baby sister for Kian!"
Kian Alexander MacKay is the couple's first child.
Afshin-Jam MacKay is an Iranian-born human rights activist, pop singer and former Miss World runner-up.
Her book, The Tale of Two Nazanins, recounts her efforts to save a 17-year-old woman from execution in Iran. She has spoken out against the ruling regime in her former homeland.
The couple married in Mexico in 2012.
You can see Afshin-Jam's tweet here.
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