Hugh Hefner claims his soon-to-be ex-wife cheated on him before their marriage failed - but that's not why he finally filed to divorce Kimberley Conrad.

The Playboy mogul decided to file, he says, after Conrad sued him in recent weeks for $5 million stemming from the sale of a home they owned together.

Kimberley Conrad, who married Hef in 1989 but had been separated from him since 1998, had been living in the house, which is located right next door to the Playboy mansion, with the couple's two kids, now ages 19 and 17.

As for why he stayed married 11 years after they essentially called off their relationship, Hef says, "At the time of the separation, I was happy to get a divorce. I only remained married for the sake of the children at her request."

He strongly denied that he owes Kimberley any money, and that he's faithfully paid her $250,000 a year as promised in a prenuptial agreement.

Frustrated, he says he's "paid every cent" that he agreed to in prenuptial and postnuptial agreements, and says "I've been generous to a fault."

Hefner notes that he was "faithful" during the time they were together, but says that Kimberley Conrad had cheated on him "early in the relationship."

He knows who the other man is, but won't say. Hillel Chodos, a lawyer for Conrad, said the filing "speaks for itself, and we'll respond in due course."

We don't know what kind of settlement these two will come to, but here's how much Hugh rakes in per month (yes, that's per month, not per year):

• Salary from Playboy: $116,667
• Social Security: $1,896
• Dividends and interest: $121,099
• Rental income: $17,058
• Income from HMH Productions: $15,808
• Pensions and retirement: $413
• Other miscellaneous income: $17,639

That's a total monthly income of $290,580. Not bad, especially on top of the $306,548 in cash and $36,802,558 in stocks and bonds he says he owns.

Guess this helps explain how an octogenarian can score Crystal Harris. Although she may not want to get her hopes up about marriage after this.