Cindy Crawford says the secret to her 26-year marriage with Rande Gerber is knowing how to 'fight nice'

• Cindy Crawford said that friendship is the foundation of her marriage with Rande Gerber.
• The supermodel added that she advises her kids to consider whether their partners make good friends.
• A study has shown that being best friends with your spouse can benefit your well-being.

Cindy Crawford has a simple answer to a successful marriage: be friends.

"That's the advice I give my kids too," Crawford told Andy Cohen on Watch What Happens Live with Andy Cohen .

"Of course, you need the other stuff — that's the fun chemistry and all that. But if that wasn't there, would you be friends with this person?" She added.

The supermodel married businessman Rande Gerber in 1998. They have two children, Presley Gerber, 25; and Kaia Gerber , 22.

Crawford said that although being married for 26 years and having kids together is hard work, the couple also respects each other and never "fights dirty."

"You got to fight nice, don't say things you can't take back," she told Cohen.

The couple's relationship started as a friendship . They first met at Crawford's agent's wedding in the early 90s. She said her agent did not want her to go to the wedding alone and gave her the choice of three guys to take. She picked Gerber.

"It wasn't a setup. I was dating someone, and he was dating someone… so we were just real with each other," she said.

Gerber was late on their first date, Crawford added.

"I'm standing in the lobby of my building, and I'm like, what the hell, you're late?" she recalled. "You know, and I have a bottle of open champagne. He had a bottle of tequila. We walked four blocks, and by the time we got to the wedding, we were like best friends."

Being friends with your spouse has benefits

A 2014 paper from the National Bureau of Economic Research in Canada found that those who named their spouse as their "best friend" were twice as likely to have higher life satisfaction.

The findings are based on data from the British Household Panel Survey, which surveyed about 30,000 individuals in the UK between 1991 and 2009. They found that married people had more life satisfaction across age groups and hypothesized that this was because spouses could lean on each other to ease the stresses of midlife challenges .

Still, Rhaina Cohen, author of " The Other Significant Others ," previously told Business Insider that investing in friendships outside your marriage is also important.

Doing so will "reduce the pressure for one person to always be the right person for every kind of need and desire that comes your way," she said.

A representative for Crawford did not immediately respond to a request for comment sent outside regular business hours.