EXCLUSIVE: Charlize Theron Reveals Her Son Jackson Really Wanted a Little Sister

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Charlize Theron adopted her second child, August, last summer, and she told ET her son, Jackson, couldn't have been happier.

After adopting Jackson, 3, from her native South Africa in 2012, Theron spent the first six months of 2015 working with an adoption agency to find another child. Theron described the process as a "family decision" and revealed that Jackson was "very specific" about his vision.

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"He was like, 'It has to be a sister, Mom. It has to be a sister,'" Theron told ET. "I was like, 'That's not really how it works. You're going to get what you get and you don't get upset.' When we got the good news that it was a little girl, we were really happy, and then he went, 'Can I now have a brother?' I was like, 'Pipe it! Pipe it!'"

It doesn't look like Jackson will be getting another sibling any time soon. At The Huntsman: Winter's War premiere on Monday, Theron told ET she's not planning on expanding her family any further.

"Both of my hands are really full right now," she said at the time. "I think I'm good for now."

WATCH: Charlize Theron Doesn't Plan on Having Any More Kids

Siblings are a major theme in Theron's upcoming adventure movie, The Huntsman: Winter's War, in which she reprises her role as evil Queen Ravenna, who betrays her good sister Freya (Emily Blunt) by freezing her heart to love.

On set, kids were frequent visitors, as Theron, Blunt and fellow co-star Chris Hemsworth are all parents to young children. Hemsworth's 3-year-old daughter India Rose took to Jessica Chastain's character, Sara, a warrior who sides with Freya in the battle against Ravenna.

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"I've been thinking about my daughter watching characters like this where they can lead armies and be in charge of their own destinies," Hemsworth told ET. "That's what I want her to think is possible -- not being rescued by the prince."

The Huntsman: Winter's War hits theaters April 22. Watch the trailer below!