PALM BEACH, Fla.  - A Florida billionaire is jumping into the increasingly congested field vying for Florida's open U.S. Senate seat.

Democrat Jeff Greene's announcement Friday comes a day after Florida Gov. Charlie Crist announced he would run as an independent.

Greene, 55-year-old Harvard Business School MB, has been largely unknown politically. But he's rubbed elbows with the infamous, having Mike Tyson as best man at his wedding and Heidi Fleiss in a guest house when she became a domestic violence victim.

Greene became a millionaire before age 30, launching a real estate empire from money he made in college from a telemarketing promotions business. He only recently passed the billion-dollar mark in net worth, making a second fortune hedging bets against the housing bubble.

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