NYC- Glamour gal Christie Brinkley kicked fourth husband Peter Cook to the curb after she found out he was cheating on her with his 19-year-old assistant, according to a published report.

The still-stunning 52-year-old supermodel learned of the affair when the teen’s cop stepfather confronted Cook in Brinkley’s presence, the National Enquirer reported on its Web site yesterday.

“He went up to both of them and said right in front of Christie, ‘If I were not worried about getting my pension, you’d be a dead man,’ ” a source told the Enquirer. “He added, ‘Stop dating my daughter.’ ”

The beautiful teen, identified by the Enquirer as Diana Bianchi, is an aspiring musician who met architect Cook, 47, while working at Stevenson’s Toys and Games on Jobs Lane in Southampton, then went to work for him.

“People have been talking about trouble in the marriage for a year. The rumor was it was somebody in his office,” Couri Hay, society editor of Hamptons Magazine, told the Daily News. “He will lose a certain amount of credibility in this town. Adultery, especially with this kind of age difference, is frowned upon in Southampton.”

Bianchi’s stepfather, Brian Pratt, a Southampton Village cop on medical leave, confronted Cook privately, but when Cook didn’t break off the relationship, he went ahead with the public showdown, the Enquirer said.

When a News reporter approached Bianchi’s home yesterday, he was chased away and threatened with arrest by a man in civilian clothes, while a uniformed Southampton cop stood by.

Bianchi’s uncle, Joseph Bianchi, told The News he knew his niece was working for Cook, but the family was shocked to hear of the reputed affair.

“The family is upset over what they heard,” he said. “I’m surprised at the news. I don’t know if it’s true or not. I guess I’ll find out.”

Nick Kraus, manager/promoter at The Stephen Talkhouse in Amagansett, said Diana Bianchi had performed at the famed club.

“She played here two or three times in 2003. She was 15. She played the keyboards in a talent contest,” Kraus said. “I thought she was very, very good, very talented and very nice. She came with her parents, who also seemed like nice people.”

The reported affair was the talk of the Hamptons last night.v “How silly of him. He was foolish,” said one of Cook’s former clients. “This really isn’t going to go over well with people here. Everyone is talking about how deliberate and underhanded it is, putting her right in his office. This is definitely a no-no in Southampton.”

Cook skipped a scheduled appearance at a House & Garden benefit in Bridgehampton last night, and a maid at the family’s gated estate said he wasn’t there.

Brinkley’s publicist had announced earlier in the week that they were separating.

Brinkley was said to be holed up yesterday in Los Angeles, where one of her parents is rumored to be ill.

“She doesn’t wish to speak about this right now,” said her spokesman, Elliot Mintz. “Christie obviously is not commenting publicly. She’s with her children. She’s shocked by all of this, of course.”