Ashton Kutcher and Mila Kunis expecting a baby boy

Ashton said: "We haven't told anyone. We're having a boy!"

And despite already having a daughter, the 'Jobs' actor says that he wasn't thrilled about having a son because he thought it would mean that his wife Mila, 33, would say no to having any more children in the future.

He admitted: "I was hoping for a girl because first of all, our first girl is unbelievable. But also I figured if we had a girl second, [Mila] might give me one more shot at having a boy and now I don't know. It's even money, she might cut me off. I want, like, 12 [children]."

The actor then insisted that he hadn't argued with the 'Black Swan' star over the size of their family, and said they were "very happy".

Whilst Ashton officially confirmed the news of their baby's sex on the late night talk show, the admission only came after he had accidentally spilled the news earlier in the day on the 'Today' show.

The 'Killers' actor told Savannah Guthrie on the show that his daughter would point to Mila's stomach and say "little brother".

Meanwhile, 'Friends With Benefits' star Mila has said she isn't worried about the pregnancy, and has stopped checking how far along she is.

She told Conan O'Brien: "I feel really good. With the first one, there were these apps where you could check daily to see the size of your baby based on fruit.

"So, 'Oh, today my baby's the size of guava, or a banana, or avocado.' And I did it, like, every day. I couldn't even tell you how far along I am right now. I'm like, 'I don't know. A couple months?' I genuinely don't know how far along I am. I'm like, 'Somewhere between this and that.'"