Christie Brinkley took the stand and delivered emotional testimony Thursday as the trial for her divorce from Peter Cook entered its second day.

Brinkley told the court she thought she had the perfect life with Cook until she learned of his affair with his 18-year-old assistant Diana Bianchi. She said her whole world was shattered upon hearing the news.

Brian Platt, a police officer and the stepfather of the 18-year-old, informed Brinkley of the affair at a 2006 graduation at Southampton High School where the model was a speaker.

He tapped her on the shoulder, she tearfully recalled, and said, "That husband of yours won't knock it off. He's having an affair with my teenage daughter."

Brinkley said she looked at Cook, sitting in the front row of the graduation ceremony, and when he shook his head in denial, she thought: "My God, it's true. He did do that."

Brinkley?s best friend, NBC correspondent Jill Rappaport, testified similarly. She said Brinkley was devastated and fragile when she learned of the affair and that she had to stay with her friend for days as she recovered.

Cook and Bianchi testified in court Wednesday. Cook took the stand again Thursday to rebut Brinkley?s testimony. The trial will pick up again Monday, July 7 after the holiday weekend.