Democratic presidential hopeful Hillary Clinton and billionaire investor Warren Buffett shake hands onstage at a fundraising event in 2007. The two will reportedly appear on the campaign trail next month. Getty Images

A Nebraska native with especially deep pockets will join Democratic presidential candidate Hillary Clinton on the campaign trail there next month: Warren Buffett. The billionaire investor and Omaha resident was set to talk tax reform with Clinton at a Dec. 16 event aimed at boosting grassroots support, the Omaha World-Herald reported exclusively Sunday. Clinton's campaign later confirmed the duo's appearance to CNBC.

Buffett, the chief executive officer of Berkshire Hathaway, Inc. and the third-richest man in the world, has publicly predicted Clinton's victory in the 2016 general election. In 2014, Buffett said he'd "bet money" that "Hillary is going to win." “I think that she is the most likely person to be president of the United States, elected in 2016, and I’m going to vote for her,” the Hill reported he said recently.

But he's also praised her rival, Sen. Bernie Sanders of Vermont. Earlier this year, the Huffington Post reported Buffett said Sanders was a "terrific campaigner."

Federal Election Commission records show Buffett has donated thousands to Clinton’s campaigns over the years. When she ran for Senate in New York in 2000, he gave her $2,000. He gifted $4,600 to her 2008 bid for the presidency, though he also donated to her then-opponent, Barack Obama. Most recently, Buffett contributed $2,700 to Hillary for America in April.

Buffett has been an outspoken proponent of raising taxes on rich Americans – something Clinton also wants. “Right now, the wealthy pay too little, and the middle class pays too much,” she said in the October Democratic debate.

Fortune noted the location of the Buffett-Clinton event was also significant, as the candidate lost to Obama in Nebraska’s caucuses in 2008.

Recent data from the HuffPost Pollster showed Clinton had the support of about 57 percent of likely Democratic primary voters, while Sanders had about 32 percent. Former Maryland Gov. Martin O’Malley was trailing them both at 4 percent.