The story of Ashton Kutcher and Mila Kunis' first kiss has left us with one big question.

It’s been 20 years since Hollywood A-listers Mila Kunis and Ashton Kutcher first met, but now the parents-of-two have confirmed how they first came to be, both on-screen and off.

Speaking to radio host Howard Stern earlier this week, Kutcher said that when the pair first kissed on the set of That 70s Show there were no fireworks whatsoever, but with good reason.

"I was 19, she was like 14," Kutcher said. "I was like, 'Isn't this illegal? Like can I... am I allowed?' It was really awkward because... she was like my little sister. I wanted to make sure she was okay."

Woah, woah, woah - IS THAT ILLEGAL?

According to Wallin and Klarich Lawyers, this would fall under California's penal code 647.6 PC, and would be a misdemeanour punishable by up to one year in a country jail and/or a fine of up to $5000.

So, uh, yes... their first kiss was pretty illegal.

The now 39-year-old added, "I think I was her first kiss, like, on the show. We have our first kiss memorialised on a TV show!"

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Their first real kiss, however, happened much later when Kutcher and Kunis were substantially more grown up.

According to Kutcher, Kunis attended a house party he was throwing and used a clever ploy to administer a kiss.

"I think I was smoking cigarettes at the time," he said, "and she had quit smoking and she was like... she wanted me to like shotgun cigarette smoke so she could breathe it in. And I started doing this and gradually through the night, it got closer and closer and closer."

Eventually, he told Stern, "I think it was pretty mutual. It was kind of obvious that things were happening."

Clearly, everything went to plan, with the pair welcoming their daughter Wyatt in 2014 and their son, Dimitri, in 2016.