Christie Brinkley repeatedly broke into tears on the second day of her divorce trial, at which her best friend described her lying on the floor, her shoulders shaking and knees bleeding after learning of her husband's infidelity, FOX News has learned.

Jill Rappaport testified she had never seen anyone as emotionally distraught as Brinkley was after the stepfather of her husband's teen mistress approached her at a high school graduation.

"That was also the day that my world was completely shattered," said Brinkley, who cried several times at the trial, which has included sensational testimony about porn, a teenage mistress and Hamptons rendezvous involving her estranged husband, architect Peter Cook.

In the following days, Brinkley stopped eating and became frail, and her children acted upset, said Rappaport, who introduced Brinkley to Cook. The two were married in 1996.

Brinkley and Cook are mainly arguing over custody of their children, Jack and Sailor, ages 10 and 13.

Video: Day 1 | Day 2 | Jill Dobson Reports

PHOTOS: Divorce Battle Begins | Christie Brinkley

The former Sports Illustrated swimsuit model testified that following her speech at Southampton High School, a man approached her and said: "'That husband of yours won't knock it off, and he's having an affair with my teenage daughter ... so I had to come to you.'"

The man was police Officer Brian Platt, the stepfather of Cook's lover, Diana Bianchi, whose affair set off a tabloid frenzy that signaled the end of Brinkley's fourth marriage.

"I can't believe it; Peter has been cheating on me ... and with a teenager," Brinkley remembered telling her friend Mindy Moak.

Platt on Wednesday testified that he told Brinkley about the affair moments after she spoke at the 2006 graduation.

"She was obviously shaken," Platt said.

On Thursday, Cook stared intently at Brinkley as she recalled the turbulence of their marriage, and he said the animated movie "Shrek" is more believable than her testimony, FOX News' Jill Dobson reported from outside the courthouse.

Brinkley also detailed owning a house in the Hamptons that she did not live in but at which she remembered finding burning candles, a refrigerator stocked with beer and wine and a dark strand of hair in an unmade bed. Cook, she said, blamed it on the gardener and said the bed had been placed there because he was planning on renting out the home.

Brinkley said after the scandal unfolded, she checked his e-mail and found a picture of Cook's naked torso with his profile for an adult Web site that finds a user's "horny match." Underneath the picture, Brinkley said, Cook described himself as a good-looking man seeking equally good-looking girls who are young and fit.

One day the couple's son, Jack, clicked on something on the computer and a porn slide show allegedly popped up, Brinkley said, adding that she quickly put papers over the screen to block his view.

"The man who I had been living with ... I didn't know who he was anymore," she said. "I felt shattered."

In the strife that ensued, Brinkley said Cook broke down crying in a phone conversation and threatened to crash his car into a tree. He denied the accusations about Bianchi, who testified that he had hidden cash for her under a rock and gave her $15,000 to help her buy a Nissan Maxima in 2005.

"That is the man who's come before this court and asked for custody of his 13-year-old son and 10-year-old daughter," said Brinkley's lawyer, Robert Stephan Cohen.

Brinkley, 54, and Cook, 49, wed in 1996. She filed for divorce a decade later, after his affair with Bianchi exploded into public view.

"There is no way to make that right," said Cook's lawyer, Norman Sheresky. "Peter has apologized. He's cried his eyes out. He's lost his marriage."

Cook and Brinkley are mainly disputing custody of the children. Her ownership of her $30 million home is not being contested because the couple had a prenuptial agreement. They are also arguing over property that includes three boats.

Brinkley fought a bid by the children's legal guardian to close the trial to the public, and Cook's lawyer said the model was partly to blame for an unseemly spectacle.

"For goodness sake: She's on her fourth husband," Sheresky told the court. "Your honor, we're here because of the self-indulgent wrath of a woman scorned."

"What kind of a mother wants her husband flogged in public?" he asked.

Cook met Bianchi, then 18, while she was working at a Hamptons toy store in 2004. He testified that he soon hired her to work at his architecture firm, paying her $20,000 to type magazine articles onto the company's Web site.

Before long, he seduced her while they were working together in the office, she testified.

"He had shown interest in me, and I reciprocated. He asked me how I would feel if he told me he was attracted to me," she said. "I wasn't taken aback, but I wasn't really against it."

Tentative and halting during an hour of testimony, Bianchi said the two had sex about 10 times before their relationship ended in late 2005. Cook counted about 12 rendezvous — some at the office, some at Brinkley's homes in the Hamptons.

Tearing up as he testified, Cook said he showered Bianchi with spending money, including $500 secreted outdoors — he said near his office; she said it was outside his and Brinkley's home. He said he slipped more cash for Bianchi behind a painting.

The $300,000 payout came in May 2007. Cook said he was trying to protect himself and his family from scandal and was concerned that Bianchi might file a sexual-harassment lawsuit. No lawsuit was ever filed.

Brinkley and Cook presented a portrait of contentment on the Hamptons social circuit. But behind the scenes, they relied on porn "to get the mood going" during the last half of their marriage, Cook said.

He acknowledged spending about $3,000 a month on pornographic Web sites in 2005. He said he has not accessed the sites since his breakup and maintained he never looked at them in the presence of his children.

Alexa Ray Joel, 22, testified that Cook treated her well before he married her mother. But she said he was constantly on her case afterward, chastising her "if I chewed too loud" and criticizing her piano playing.

"He was just very critical of me in general," said Joel, a singer, songwriter and pianist. Brinkley said Joel has a deviated septum, which causes her to chew with her mouth slightly open.

Joel, Brinkley's daughter with "Piano Man" Billy Joel, said Cook once shoved her head into a bucket of water after a leak from her shower trickled into the kitchen in 2003.

Cook stormed into the bathroom and demanded she mop up immediately, Joel testified. When she got downstairs wearing only a towel, he pushed her head into a bucket and yelled, "You clean this up!" she said.

When Brinkley found out, "she was horrified," her daughter said.

When questioned if she was aware of the confrontation, Brinkley said she was and it was not the only shower incident. She said she insisted Cook see someone about getting help stopping his constant criticism of the girl. He did, she said, and the criticism stopped, but it was fleeting.

Cook initially denied the liaison, but he has since apologized and argues it should not disqualify him from getting custody of his children.

Cook denied Joel's account when he returned to the stand Thursday, saying he had "absolutely not" pushed her into the bucket. He said he tried to stop her "loud, aggressive" piano playing only when his and Brinkley's younger children were going to bed and was only backing up Brinkley's own admonishments about her daughter's chewing and protracted showers.

Cook's lawyer tried to portray Brinkley's testimony as courtroom theater.

"If you want to call me an actress, that's fine," Brinkley replied.

"I'm no Meryl Streep, but I have been in a very successful movie," she said with a sheepish smile while referring to 1983's "National Lampoon's Vacation."

"Thirty years later, it's still got legs," she said.

Brinkley's lawyer called her a doting mother whose work schedule revolves around her children.

Cook's attorney also painted his client as a good parent, noting interviews in which Brinkley referred to him as "the best dad in the world."

"I thought I had the picket fence," Brinkley said. "I thought we were happy."

FOX News' Jill Dobson and The Associated Press contributed to this report.