Bush has struggled to gain traction. (AP Photo/Terry Renna, File)

The billionaire insurance magnate whose company gave $10 million to the super PAC behind the Jeb Bush presidential bid  expressed regret Thursday about the direction of that campaign.

"Listen, I like Jeb Bush," Maurice R. "Hank" Greenberg told a Fox News correspondent late Thursday morning, just hours after the donation was first reported. "Sorry he's not living up to expectations, but that's the reality of it."

Greenberg's mega-donation, first reported Thursday by the Wall Street Journal, puts him in a rarefied group of donors who have contributed double digit millions to a politically-oriented organizations so far this campaign. A handful of donors who have given to super PACs supporting the presidential bid of Sen. Ted Cruz (R-Tex.), including Robert Mercer, the New York hedge fund executive, who gave $11 million; Toby Neugebauer, a private equity company founder, who gave $10 million; and members of the Wilks family, energy entrepreneurs in Texas, who gave $15 million. With the revelation of his eight-figure contribution, Greenberg became by far the largest known donor to Bush.

Greenberg made his fortune building American International Group, the insurance and investment giant that received a government bailout several years ago, after Greenberg had left. It is not known when Greenberg's current firm, C.V. Starr and Co., made the donation to support Bush. A spokesman for the Bush super PAC, Paul Lindsey, declined to address the report, saying that "we do not discuss donors." Those details will still emerge by the end of the month, when the next Federal Election Commission reporting period ends on Jan. 31.

Alice Crites contributed to this report