Speaking to Ellen DeGeneres during a Mother's Day-themed edition of her chat show, Mila spoke about how she kept news of her pregnancy under wraps for some time.
"You hid it for a while," said Ellen, 56. "You got away with it for a long time."
"I did," replied Mila. "We were actually able to for a very long time, it's amazing."
Mila, who will not confirm when the baby is due or what gender it is, did reveal that she and Ashton have already chosen a name for their little one.
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The 30-year-old star, who is engaged to Two and a Half Men actor Ashton, 36, also spoke about how he has been helping her with her cravings for "vinegar-based foods" such as Sauerkraut and pickles.
Mila Kunis chatting to Ellen DeGeneres
"He kind of pre-empted this," she said. "He assumed that I was going to have goofy cravings.
"He stocked our secondary fridge with weird food like pickles and Sauerkraut and anchovies and ice cream so that if at some point during this pregnancy I really want something.
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"And it happened last week!" She added. "I was like 'oh my god I need a pickle' it was the weirdest thing I really needed this pickle and he was like 'hold on a second' and disappeared in the back yard and came back with the most amazing dill pickle of all time."
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Mila, who is fluent in Russian thanks to her Ukrainian upbringing, said Ashton is also learning the language so they can speak to their new arrival in the East Slavic language.
"He's been taking classes for like six months now," said Mila. "He does it twice a week, a woman comes to the house and gives him lessons."
Mila is hoping to have a natural labour, without an epidural.
"I'm going to do it as natural as I can, unless there's an emergency," she said. "I know, I'm crazy, but I did this to myself I might as well do it right."