A rep for the "Cinderella" star -- Blanchett plays the evil stepmother in the upcoming film -- confirmed the adoption to People on Friday.
The tyke's name is Vivienne, according to Australia's Women's Weekly, which first reported the news earlier this week. The 45-year-old actress had been spotted toting her new daughter while picking up her sons from school, the outlet said.
Blanchett and 49-year-old Upton, currently artistic director at the Sydney Theatre Company, were already parents to Dashiell John, 13, Roman Robert, 10, and Ignatius Martin, 6.
So Vivienne makes one more kiddo who might soon be watching mom and dad work.
"They've watched a lot of shows from the wings," the "Lord of the Rings" actress said of her sons in a 2013 interview with the Independent. "What I really loved is they see the hard work that goes into it. They can see the crew pulling the strings. They can see the teamwork.
"That's a really good thing for them to see -- that it's not just about the famous face at the front."
A Blanchett rep did not immediately respond to a request for comment.