On Friday, Hefner filed documents in L.A. County Superior Court seeking to dissolve their marriage, citing "irreconcilable differences." The docs say they were married on July 1, 1989 and have been separated since January 12, 1998.
Hefner had been supporting Kimberly and their two sons, who have been living in the house next door to the Playboy mansion.
But things got rocky this year when Hef sold that house, and then Conrad sued Hef -- accusing him of screwing her out of more than five million bucks.
UPDATE: In the docs, Hugh is asking the judge to set spousal support at $20,000 per month -- justifying such a small amount by saying he's already given Kimberly close to $12 million since their 1998 separation.