Billionaire industrialist and major GOP donor David Koch won't donate to the Republican National Convention in July, where Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE will officially receive the party's nomination for president, Bloomberg reports.

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Koch gave $1 million to support the party's 2012 convention but won't even attend this year's gathering, another signal from the GOP megadonor that he doesn't support Trump.

His brother Charles told USA Today this week Trump would have to change his stances on a number of issues to win his support and called his comments about a judge's Mexican heritage "unacceptable." Bloomberg reported that Charles Koch won't donate to the convention effort either.

"It's either racist or it's stereotyping," Charles Koch said of Trump's comments. "It's unacceptable, and it's taking the country in the wrong direction."

Asked if he thought Trump was fit for the presidency, he said: "I don't know the answer to that."