The 34-year-old British actress confirmed during Friday's episode of BBC Breakfast that she recently welcomed her second child with husband James Righton.
Knightley was discussing her new film Official Secrets when she momentarily lost focus in the interview.
"I can't remember what your question was. You can tell I've got a six-week-old baby, haven't you? I'm talking but I have no idea where I'm going," the star said.
"Can I just say this is about the third time since I've given birth that my hair has been brushed?" she added with a laugh. "And I didn't brush it. Lovely Luke, who is my hairdresser today, he brushed it."
Knightley was in the midst of a six-hour work day. She said she's been busy pumping breast milk and had to return home by 6:30 p.m. to feed her newborn.
"Everyone has to deal with pumping. If you're doing that, and if it's working and you want to do that and if you can do that, then yes, we're pumping," the actress said.
News broke in September that Knightley had welcomed her second child. The actress and her husband are also parents to 4-year-old daughter Edie.
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Knightley plays whistleblower Katharine Gun in Official Secrets, co-starring Matt Smith and Matthew Goode. The film recounts how Gun leaked a secret memo exposing an illegal spying operation by the U.S.
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