Story highlights T. Boone Pickens, always a top target for Republican fundraisers, said he's backing Donald Trump

Pickens addressed reporters on the sidelines of a hedge fund conference in Las Vegas on Wednesday

Las Vegas, Nevada (CNN) Top Republican donors may be taking their time flocking to Donald Trump, but a prominent billionaire is on board: energy and hedge fund magnate T. Boone Pickens.

Pickens, speaking to reporters on the sidelines of a hedge fund conference in Las Vegas, said he talked to Trump Monday and confirmed to the New York billionaire and presumptive nominee he'd support his candidacy.

That's no small thing for Trump, whose presumptive position atop the GOP ticket has brought a new reality to his plate: the need to help raise hundreds of millions of dollars for his campaign and others across the Republican Party.

Pickens, always a top target for Republican fundraisers, regularly sends big checks to Republican causes and candidates in Washington, from members of Congress and presidential campaigns to various state parties. He wasn't initially on board with Trump, however.

"I didn't think he was serious," Pickens said Wednesday on the sidelines of the SALT Conference, which is considered one of the hedge fund industry's premiere conferences. Pickens was an early backer -- to the tune of $100,000 -- of former Florida Gov. Jeb Bush. He then looked to back Carly Fiorina and Ben Carson -- something Trump didn't hesitate to mention during the phone call this week between the two, Pickens said.

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