April 20, 2007 -- Christie Brinkley's cheating husband has apparently paid off his sultry young mistress - whom he bedded after he hired her at his Hamptons architectural firm, The Post has learned.

But details of the settlement between philanderer Peter Cook and 20-year-old aspiring singer Diana Bianchi - including how much money he may have given her - remained secret yesterday.

"The matter has been resolved. That's all I'm permitted to disclose to you," said Bianchi's high-powered sex-harassment lawyer, Rosemarie Arnold.

Cook's lawyer, Kathleen McKenna, did not return a message left at her firm, Proskauer Rose.

The deal spares the 48-year-old Cook the embarrassment of Bianchi revealing in public court filings the lurid details of their affair, which began when she was just 18.

The deal was inked after what apparently were months of confidential settlement talks, and nearly a year after Bianchi's lawyers put the caddish Cook on notice that they were more than willing to sue him.

The disclosure last summer of Cook's trysting with Bianchi promptly spurred supermodel Brinkley, 53, to split from the amorous architect after 10 years of marriage. Brinkley later sued her horndog hubby - her fourth - for divorce, a court case which remains pending. Bianchi told The Post last year that she first caught Cook's roving eye when she was a 17-year-old clerk at a tony Hamptons toy store, where the dad of two was shopping.

Cook later hired her in spring 2005 to work at his firm in Southampton, to maintain its Web site and perform other tasks.

"He first physically made advances at me," Bianchi said last year, "probably a month after I started working there."

Although their affair was consensual, one of her lawyers, Joseph Tacopina, last year crowed that she had "a great sexual-harassment claim."

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