He Cheated on Christie Brinkley?

July 19, 2006— -- At age 52, supermodel Christie Brinkley is still one of the most beautiful and most photographed women in the world, but that didn't stop her husband from apparently cheating on her.

Brinkley's world was turned upside down when she reportedly discovered that her fourth husband, architect Peter Cook, was cheating on her with his 19-year-old employee, Diana Bianchi. Brinkley announced last week that she and Cook had separated.

On the surface, it doesn't seem to make sense that a man would cheat on such a beautiful and successful woman. But experts say the reason it happens to supermodels is the same reason it happens to anyone.

"Beauty, wealth and celebrity are no guarantee against an affair," said psychoanalyst Bethany Marshall. "The best insurance policy is to be in a relationship with a man who loves you and where there's a really good attachment."

Marshall said men -- especially those dating successful women -- will sometimes feel a need for power.

"They'll often seek younger women where they can feel powerful and be the big cheese," she said.

In Brinkley's case, she reportedly first learned about the affair from the teen's stepfather, and then confirmed Cook's affair through checking his e-mails.

Bianchi told Fox News' New York affiliate that her relationship with Cook began a year ago. She said he lavished her with gifts and cash.

"He made the advances verbally toward me first and then I guess it just escalated," she said. "He didn't say he would leave her. He just basically left it at he wished he was younger or he wished we had met at a different time."

Celebrity observers are stunned by the Brinkley-Cook breakup not just because of Brinkley's supermodel status but also because the marriage seemed strong.

"People are shocked to hear this story," said Us Weekly magazine style editor Katrina Szish. "First of all, Christie and Peter's marriage seemed rock solid and second, who cheats on Christie Brinkley?"

Brinkley isn't the first beautiful and successful woman who has been cheated on.

The late Princess Diana complained about the attention Prince Charles paid Camilla Parker Bowles. The Prince and Bowles married last August.