But, she explained, one day, their friendship simply turned into something more.
"All of a sudden, it wasn't the same. And I was really proud of myself for acknowledging that," Kunis told Marie Claire magazine. "The best day of my life so far was the proposal. I cried. I was a mess. Not to discredit any relationships in my past, but this relationship is different."
Kunis, 30, and Kutcher, 36, are now expecting their first child. (And no, you should not say "they're pregnant," Kunis cautioned Jimmy Kimmel recently.) And though Kunis has said that she's planning a natural birth, she's realistic about what the delivery process will be like.
"Two people are allowed in my delivery room. My doctor and my significant other. And he is staying above the action," she said bluntly. "He'll be head to head. ... Unless he wants to risk his life and see. But I wouldn't if I were him!"
Going forward, she's determined to make sure that their child is raised to be well-behaved and respectful.
"I just don't want my kids to be a**holes. I feel like so many kids nowadays are," she said. "Both of us just want to have well-behaved, honest, nice children who people meet and say, 'That's a good kid.'""