• Mila Kunis says knowing Ashton Kutcher since her teens has made their marriage easier.
• That's because they both already knew "the good, the bad, the ugly" about each other, she said.
• Moreover, their long history has given them confidence that they can continue evolving together.

Mila Kunis says years of growing up together taught her and Ashton Kutcher to embrace change in their relationship.

During an appearance on "The Drew Barrymore Show" on Sunday, Kunis said reconnecting with Ashton Kutcher in her late 20s came with a unique advantage: They already knew each other's history. The pair first met while starring on "That '70s Show" as teenagers.

As a result, neither had to explain how they had changed over the years.

"He knew me through all of them, and I knew him through all of it, through like the good, the bad, the ugly, you know, and vice versa," Kunis told host Drew Barrymore. "So, when we reconnected, there was no getting to know each other, but let me tell you all these hidden secrets. Let me tell you about all my baggage."

There was "nothing to hide" between them, she added.

"Our fundamentals, our foundation, everything is built on respect because we've known each other since I was 14 and he was 19," Kunis said.

After reconnecting, Kunis and Kutcher married in 2015. They have two kids together.

She added that knowing each other for so long has made it easier to embrace change within their relationship.

"It's seeing that people can grow and evolve. It's also just knowing that at all moments in our lives we will be able to grow together because we already have," Kunis said.

She doesn't worry about whether Kutcher will like the person she's becoming, she said: "He's not going to go, 'Well, that's not the person I married.' He'll be like, 'OK, let's go for a ride.'"

Kunis is not alone in that view. Other celebrities have also said that long-term relationships require accepting that a partner will not always be perfect — or stay exactly the same.

Goldie Hawn has said that while she and Kurt Russell don't love everything about each other, they don't view those differences as dealbreakers.

"Why is that a reason to break up? Why is that a reason to say this isn't working?" Hawn said.

Seth Rogen has said that the key to his 15-year marriage is accepting that people change.

"Sometimes your partner changes with you, and you have several relationships with the same person that have new parameters, new boundaries, and new guidelines that are reflective of who you are as you become different people," he said.