NYC- Knockout teen Diana Bianchi. broke her silence yesterday to say Christie Brinkley’s philandering hubby lured her to his business with the promise of a doubled salary – then seduced her with feverish fawning.

“I feel like I made a lot of mistakes,” the 19-year-old told Fox 5 News. “I feel like I just wasn’t thinking straight. I got flattered and caught up in things.”

Bianchi, wearing a polo shirt and lip gloss, said she met Peter Cook while working at a Southampton toy store when she was 17 – and that he quickly seized on her vulnerability.

“I needed a job, and he told me he would double my salary,” she said of her low-level job at Cook’s architecture firm.

“I knew he was married. I mean, there were pictures of his family in his office everywhere. I never expected that he would take it to a different level.”

A high-school grad looking to bolt her parents’ house and make it as a pop singer, Bianchi apparently was easy prey for a slick Lothario. She described herself as “a little too trusting sometimes.”

“He’d make advances toward me at first and then I guess it just escalated to something that I didn’t really expect,” she said.

“He said he was unhappy, he was looking for something new or different,” she told Fox 5 News’ Rosanna Scotto. “He said he wished things were different. He wished he were younger or that he had met me at a different time.”

Bianchi said Cook never “promised that he would leave” Brinkley, his wife of 10 years.

“I never asked him to leave her for me,” she said. “I never was in it for that. I didn’t have any kind of intentions like that.”

She said Cook, 47, ponied up the down payment last year for her white Nissan Maxima, but “everything has always been in my name because I guess he didn’t want any affiliations.”

Sources in Southampton said Bianchi also dated her school’s handsome star athlete Sean Keckeisen during her liaison with Cook. But the high school sweethearts were separated when Keckeisen left to complete his senior year outside the area.

Keckeisen declined to comment yesterday as he and friends rode surfboards on the Southampton shore.

“She always had [Sean] in her car. It was always her driving out here to see him,” said a clerk at a local deli. “They’d hold hands, they’d kiss. She said he was her boyfriend.”

Meanwhile, Brinkley, the former wife of singer Billy Joel, remained mum as she tended to her sick mother in California.

The supermodel, still gorgeous at 52, first got wind of Cook’s cradle-robbing infidelity when Bianchi’s stepdad, a Southampton Village cop, approached her June 25 at Southampton High’s commencement ceremony, where she lectured grads on the dangers of global warming.

Bianchi’s lawyer Joseph Tacopina said Cook went to great lengths to hide his indiscretion – once driving all the way to Brooklyn to leave a note on her car. Cook also left money for Bianchi in hidden places around Southampton, the lawyer said.

“He’d tell me like if he was going to leave it somewhere for me, but it was never like a scheduled thing,” Bianchi said.

Cook did not return calls seeking comment, but his mother said she’d like to see a reconciliation.

“I have heard about it. The whole family supports Peter, and we certainly hope he and Christie get back together again,” Jean Cook, 82, told the Daily News.

Bianchi, who’s mulling a sexual harassment lawsuit against Cook, also has a hope: That the celebrity scandal doesn’t ruin her chances at pop stardom.

NY Post version: The beautiful teen lover of Christie Brinkley’s hubby yesterday revealed in sensational detail how the seamy spouse secretly seduced her by first playfully brushing up against her at work – then writing a saucy come-on note saying he lusted after her.

Diana Bianchi recalled how she met randy dad of two Peter Cook when she was a 17-year-old clerk at a tony Hamptons toy store – and how things quickly became sexual between the hot pair after he offered her a job at his architecture firm.

At first, “basically, he would slip in little comments and stuff,” said the now-19-year-old knockout, referring to how Cook would notice her appearance.

“He first physically made advances at me . . . probably around a month after I started working there . . . He just started being physically around me more and physically closer to me more,” Bianchi said in a stunning, 45-minute interview with The Post.

Bianchi – an aspiring singer from Southampton – couldn’t even bring herself to call her former lover by his first name yesterday.

She admitted that at the time Cook started putting the moves on her, she was “a little naive” and not “really thinking it’s like that.”

But the caddish Cook, 47, soon became bolder, suggestively rubbing up against her and touching her arm at times – while the pair worked together near a picture of his supermodel wife.

The panting hubby then laid all of his cards on the table.

“One time, I was standing at the desk, and he was doing something on, like, Microsoft Word, and he wrote, ‘How would you feel if I told you I was attracted to you?’ ” Bianchi, then 18, recalled.

“And I was like, ‘Uh, I dunno.’ I didn’t really answer him. I was kind of thinking, ‘Are you serious? Are you kidding?’ I really didn’t know what to do at that point.”

But the conniving Cook continued to aggressively woo her over the next few weeks, assuring her that his famous, 10-year marriage to supermodel Brinkley was already on the rocks.

“We started talking about things, and he was telling me that he was unhappy and that he was having problems at home,” Bianchi said.

They soon began sleeping together – although, she said, “We were not out dating [in public]. We didn’t do anything like that.”

Still, “I felt uncomfortable,” the teen admitted. “I had never been with anyone who was married. I was always on the right track. This was all new to me.”

Eventually, the strain of sneaking around with Cook got to be too much, Bianchi said, and she broke up with him in April.

“I just . . . it was uncomfortable for me,” the teen said with a heavy sigh.

Asked how Cook handled the breakup, Bianchi said, “I guess not well,” referring to his repeated attempts to woo her back with notes and phone calls, to no avail.

The Hamptons native said she has been “hearing that I’m not the first person that this was happening with,” noting that pals have told her Cook had trysts with other young women as well.

“I guess . . . there’s a lot of other girls in this position right now, and it’s not a good place to be,” Bianchi said.

“We were all tools of his little game, I guess,” the petite brunette said.

Bianchi said she now believes that Cook – despite the sweet words he whispered to her during their relationship – had been interested in getting only one thing from her: sex.

Bianchi spoke with The Post at the office of her high-powered lawyer, Joseph Tacopina.

Tacopina said he’s been hired in case Bianchi is called as a witness in what could end up being a bitter, $60 million divorce between the 52-year-old “Uptown Girl” Brinkley and Cook, her fourth husband.

But the dapper lawyer also is exploring the possibility of filing a civil suit against Cook.

Bianchi has “got a great sexual-harassment claim,” said Tacopina, who has teamed with expert sexual-harassment lawyer Rosemarie Arnold for the potential case. “He hired her to bed her. He used her, abused her.”

Cook, whose separation from Brinkley was announced by the model last week, did not return a call seeking comment yesterday.

Bianchi is the stepdaughter of Southampton Village Police Officer Brian Platt.

Platt confronted the amorous architect several times about having designs on his daughter and demanded that he stop, but Cook brushed him off.

Platt finally approached Brinkley at Southampton HS’s recent graduation, where she was speaking, and told her about the affair. The wronged wife soon confirmed the adultery through steamy e-mails that Cook and Bianchi had sent to each other.

Brinkley’s spokesman, Elliot Mintz, yesterday said, “To the best of my knowledge, I don’t believe Christine ever met the girl.”

Mintz also said Brinkley is “just a woman who at this moment is completely preoccupied with the protection of her children, trying to isolate them from all of this coverage, and trying to heal.”

She and Cook have two young kids: 8-year-old daughter Sailor Lee and Jack Paris, 10.

Standing barely 5 feet tall and dressed casually in a green polo shirt, knee-length jeans and sandals, Bianchi looks younger than her age.

Yesterday, she sported a green heart inked on her wrist that appeared to be a tattoo, but she said it actually was a pen drawing done by her little sister.

She was shy and nervous discussing the intimacy between her and Cook.

Bianchi said she first met Cook in the summer of 2004, while she was working in Stevenson’s Toys and Games on Jobs Lane in Southampton for $12 an hour.

Cook was there to buy toys for his two kids.

“He used to come in the store all the time when I was there,” Bianchi said. “I didn’t know how old he was at first.”

Although Cook made a point of speaking with her during each visit, Bianchi said she was oblivious to his apparent interest.

“I didn’t notice if he was [interested],” she said. “I never thought that he would be or that he should be.”

But her co-workers were more perceptive in noticing Cook’s eyes focusing on Bianchi.

“People around me were like, ‘Oh, he’s coming in here a lot.’ I didn’t really take it into consideration,” she said.

Bianchi left Stevenson’s when it closed for the sea son – and Cook soon made her an offer. He proposed that she come to work for him at his firm, Peter Cook Architect, on Elm Street in Southampton.

Bianchi joined the firm in the spring of 2005 to work on its Web site and to do “text for it and articles and office work and just basically whatever needed to be done.

“I needed the money, I needed a job,” she said.

“I had just moved out of my house, I was trying to do things on my own,” she said. “I didn’t want [my parents] to think I couldn’t do it on my own.”

Bianchi knew at the time that Cook was married to Brinkley – a still- striking blonde and at one time, the muse of her third husband, superstar singer Billy Joel.

A large photo of Brinkley and the children hung just above Bianchi’s desk in the office.

“It was alright at first, it was just typi cal,” Bianchi said of her job. “I didn’t have a problem working there.”

But when pressed on when she began reciprocating Cook’s advances, Bianchi paused.

“I don’t like these questions,” she said.

She then left Tacopina’s office to confer with the other lawyer, Arnold, for sev eral minutes.

Before she returned, Tacopina confirmed that Bianchi and Cook had a sexual relationship, which spanned about one year.

But the lawyer also said, “I’m just not going to let her” answer questions about how many times she slept with Cook, where it occurred and other circumstances of the trysts.

Still, Tacopina did say Cook began plying her with gifts of cash totaling up to $1,500 per month – on top of her eventually $50-per-hour salary – as well as paying for her new Nissan Maxima and “jewelry all the time.”

But the stress of having a personal relationship with Cook while working for him began to take its toll, Bianchi said, so she began working from home.

When she broke things off, Bianchi was living with her older sister in Bensonhurst in Brooklyn, and Cook “kept trying to get in touch with me. He kept e-mailing me and calling me.”

Cook would leave messages saying, “Call me. Are you OK? Please call me,” Bianchi said.

“And I wouldn’t call him back.”

Several times, Bianchi said, Cook drove to Bensonhurst to leave notes for her on her car, asking her to get in touch with him. But she refused to do so even though his desperation was apparent “if he was going to drive all the way to Bensonhurst.”

“I guess he was disappointed,” she said.