Conrad, 47, is the mother of two of Hefner's four children, and had for years been supported by him in a home next to the Playboy mansion.
Hefner tells PEOPLE he isn't ruling out another walk down the aisle someday. "It's unlikely since I haven't been very successful at it. But anything is possible," says Hefner, who is currently dating Playmates Crystal Harris, 23, and twins Karissa and Kristina Shannon, 19.
Hefner decided to file for divorce, he says, after Conrad sued him in recent weeks for $5 million stemming from the sale of a home they owned together. He strongly denied that he owes Conrad any money, and that he's faithfully paid her $250,000 a year as promised in a prenuptial agreement.