Together for more than forty years, Goldie Hawn is getting candid about why her relationship with Kurt Russell is so successful.

On Friday, while celebrating the 20th anniversary of The Goldie Hawn Foundation and MindUP, the actress revealed a key element to their love story.

"You have to have good sex," the 78-year-old said bluntly in an interview with E! News.

KURT RUSSELL, GOLDIE HAWN KISS DURING ROMANTIC ASPEN GETAWAY AFTER 40 YEARS TOGETHER

Goldie Hawn in a black sparkly blazer with white lapels looks to her right on the carpet with Kurt Russell in a black suit and blue tie

Goldie Hawn says "good sex" is an important component in her relationship with Kurt Russell. (JC Olivera/Variety via Getty Images)

"Because sex is something that connects you and creates more belonging. People who have healthy sexual relationships usually last a lot longer. But it's not just because of the act, it's because of the warmth and the intimacy that it creates," she explained. 

"You have to be nice to each other upon occasion," she teased.

Although Hawn said having that intimacy is important, it's also the time spent recognizing your differences that really makes a relationship stick.

Goldie Hawn in a patterned dress hugs and kisses Kurt Russell in a grey patterned shirt

Goldie Hawn and Kurt Russell share a kiss. (Goldie Hawn Instagram)

"People who have healthy sexual relationships usually last a lot longer. But it's not just because of the act, it's because of the warmth and the intimacy that it creates."

— Goldie Hawn

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"You know you're not the same person," the "Overboard" actress said. "You don't think the same way oftentimes. And you have to accept that, but you have to measure are we having fun, or is this something we want to do? Do we have laughs together? Do we share certain things? You don't have to share everything."

"We have a lot of expectation, I think, around relationships, but you have to like the person. That's very important."

Goldie Hawn and Kurt Russell give each other a kiss on top of a rock

Goldie Hawn and Kurt Russell first crossed paths on the set of their film, "The One and Only, Genuine, Original Family Band," which premiered in 1968. (Goldie Hawn Instagram)

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Russell, 73, had his own take on why he and Hawn had seen such longevity in their relationship.

"Most people that have been together for a long time, I think, share one thing in common," he told the outlet. "And that is that after that many years together, you will have experienced just about everything there is to experience together and understand all the ups and downs and what it means."

"I just love the fact that we met and [we're] still doing it. We still like being together." 

Kurt Russell in a tuxedo and Goldie hawn in a black dress in 1990 in New York City

Kurt Russell and Goldie Hawn began dating in 1983. They have raised their children from separate relationships together. (Catherine McGann/Getty Images)

The couple originally met on the set of their film, "The One and Only, Genuine, Original Family Band," but didn't get together until years later. Work brought the duo back together in 1983, for their film "Swing Shift." 

Hawn and Russell, who each have their own children from previous marriages (Kate and Oliver as well as Boston, respectively), share one son together, Wyatt. 

During a March appearance on Dax Shepard's podcast, "Armchair Expert," Hawn spoke extensively about her relationship with Russell and the obstacles they overcame as a couple. 

"We don't agree on certain things. He was tougher than me as a parent. … But we have a very, very strong family because of it," she said. 

"That was one of the things that gave us things to talk about," she said of why their relationship stuck. 

Kurt Russell in a white shirt and Goldie Hawn in a blue printed dress pose for a photo

Kurt Russell says most relationships that have lasted as long as his with Goldie Hawn are successful because the people in them experience "just about everything there is to experience together." (Matt Winkelmeyer/Getty Images for Netflix)

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The couple is also famously not married.

"I think that if we were married, there probably could have been times, when you go, ‘Oh c’mon. I'm done,'" she told Shepard. Still, Hawn said, "I'm really happy I stayed."