David Koch, the billionaire industrialist backing Mitt Romney's bid for the White House, disagrees with the candidate's position on gay marriage.

Koch and his older brother Charles co-own Koch Industries, the second largest privately held company in the United States. They have donated heavily to several political advocacy groups, including the pro-Republican Americans for Prosperity, which David Koch chairs.

In an interview with POLITICO.com from the Republican National Convention, Koch, who served as a delegate from New York, said, “I believe in gay marriage.”

When asked about Romney's opposition to such unions, Koch replied, “Well, I disagree with that.”

(Related: Mitt Romney, Paul Ryan touch on gay marriage at RNC.)

Koch, the 1980 vice presidential nominee for the Libertarian Party, also said he now considers himself a Republican.

“The Libertarian Party is a great concept,” he said. “I love the ideals, but it got too far off the deep end, and so I dropped out. I think the Republican Party has a great chance of being successful and that's why I support it. … But I believe in the libertarian principles.”