The 44-year-old actress is a mother of three, having welcomed a boy with fiancé Old Green in May, and told Harper's Bazaar magazine she has no problem if he needs food - regardless of where she is or who she's with.
"When you have a baby and you're breastfeeding a baby which I still am, hence the brain not here," she said.
"Well, the respect for your body for your body, in my case, became enormous.
"And then if your body is feeding your baby and people have an issue with your boob, it bothers me because it's a you issue. I'm feeding my child.
"If you need to feed your baby, feed your baby, and everybody else has to grow a pair and deal with it, it's a breast."
Miller says "everyone's seen them at this point" because she's "a bit bohemian".
"And if the baby's hungry and I'm at dinner, yes I'm going to whip my boob out and feed the baby and everyone's cool with it," she said.
"So free the nipple!"
Miller is also mother to 14-year-old daughter Marlowe with ex-partner Tom Sturridge and another daughter with Oli, who was born in January 2024.
She hasn't revealed the names of her middle child, or her latest arrival.
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