Christie Brinkley details moment she learned husband Peter Cook was having an affair with an 18-year-old

Christie Brinkley is calling out her cheating ex-husband, Peter Cook.

In her new memoir “Uptown Girl,” the 71-year-old supermodel described her marriage to the architect as “the most tortured relationship” she’s ever had, and recalled learning of Cook’s affair with an 18-year-old in 2006.

Brinkey, per People, wrote that she was giving a graduation speech at a local high school in the Hamptons when a random man approached her and exposed Cook’s infidelity.

“Excuse me. I need to tell you that arrogant husband of yours has been having an affair with my teenage daughter,” the man allegedly told Brinkley.

“I was so stunned that I froze,” Brinkley wrote, adding that she immediately looked out into the crowd where Cook was sitting with their son Jack, 29.

“Peter’s eyes were already trained on my face, as he began shaking his head, ‘No,”‘ she said.

“When your whole world falls apart and you realize in a heartbeat you’ve suddenly become the cliche middle-aged woman whose husband is having an affair with a much (much) younger woman, what do you do?” she asked.

Brinkley explained that she knew Cook was “guilty” from his reaction at the graduation.

“In that moment, I thought I was going to pass out onstage, in front of hundreds of people,” she recalled. “When I stood back up, I asked the man for his card, but he told me he didn’t have one and that he was a police officer in town, so all I had to do was to go into the station if I wanted the full story.”

Brinkley said that two of her friends helped her search her and Cook’s family computer where they discovered a “labyrinth” of files, including “a panoply of incriminating photos and porn accounts.”

“It was so insane that it was almost funny and soon enough, the three of us were doubled over in laughter, as printouts of girls in X-rated poses began piling up on the floor faster than trash outside a greasy takeaway,” she wrote.

Brinkley and Cook’s split led to a six-year divorce and custody battle. They welcomed daughter Sailor, 26, during their marriage, while Cook adopted Brinkley’s son Jack, whom she shares with ex Richard Taubman.

“I kept saying I don’t understand what good was a prenup?” she recalled in her memoir. “It was exhausting and scary because I always lived in fear of them taking my kids because that was the constant threat and a terrifying thing to live with.”

“I got a prenup so I didn’t have to go through all this but still did. It was mind boggling and it was hard to write about,” she added.

Brinkley, who won full custody of Sailor and Jack, wrote that she wasn’t sure if she “would ever recover” from her and Cook’s tumultuous breakup.

“Whenever I felt this, I stopped, looked inward and counted my blessings,” she said, “which was a long list that always started with Alexa Ray, Jack, and Sailor.” (Brinkley shares daughter Alexa Ray, 39, with ex Billy Joel).

She added of her children supporting her memoir, “They said it’s your story to tell, so tell it.”