No details of the birth have been released yet. (E! News was first to report.)
The happy couple, who married in July 2015 after three years together, announced in June that they were expecting another bundle of joy to join their firstborn, 2-year-old daughter Wyatt.
In October, Kutcher, 38, accidentally revealed the sex of their second baby during an interview on the Today show. A day later, he almost let slip his unborn son's name while guest-hosting Live With Kelly.
"No way people heard that," he said after whispering the name to Kelly Ripa without realizing that his microphone was still on. "I thought it was over! I would have been murdered. The wife would have taken me out!"
Kunis, 33, meanwhile, already has baby No. 3 on her mind. "I think you know when your family is complete," she told Ryan Seacrest in July. "After we had Wyatt, the second that I gave birth, I was like, 'I know that we need to have another baby.' We both knew it; we just felt it. And so I always say after the second one, we'll know if we need to have another one. I really do believe you know when your family is complete."
The Ranch actor and the Black Swan actress met on the set of That '70s Show in 1998. They were close friends for years before they started dating in 2012, several months after he split from then-wife Demi Moore.
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