Halle, who is now 47, revealed she was caught off guard when she and husband Olivier Martinez found out she was pregnant, because she had been feeling 'premenopausal.'
The X-Men actress welcomed her second child, Maceo, seven months ago.
"I didn't think it was possible to have another baby," Halle told chat show host Ellen DeGeneres in a new episode airing today (Tuesday, May 20).
"'They call it a geriatric pregnancy," she added. "This is probably way TMI, but I was really, you know, kinda premenopausal, so to have this happen was a huge shock."
Halle credits her 'miracle' pregnancy as being the result of the prayers of her six-year-old daughter Nahla, whose father is Canadian model Gabriel Aubry.
"Nahla prayed and prayed for him, for like a year and a half," she said. "For a baby and a bunk bed and she got both of those things!
"Only her prayers could have done this. I didn't think it was possible at my age, honestly."
Taking about Nahla's relationship with Macro, Halle said:
"He's like one of her dollies that came to life. All she wants to do is change his clothes. Like she'll purposely like throw something on his shirt and say, 'Oh mommy, he's got to change his shirt. He has a mess on him!'
"She just likes to change his clothes, change his diapers...'
Despite having a little helper to assist with changing duties, Halle admits that some things have been tougher the second time around - and she puts this down to gender differences.
"There's a difference between boys and girls," she told Ellen. "I breastfed Nahla and I'm nursing my baby. When I would put Nahla on the boob she would go (light sucking) a nice little girly suck, with him it's like (chomping suck). He's like sucking the life out of me. So I see the difference between boys and girls!'
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