Republican megadonor David Koch is stepping down from his roles at Koch Industries and its affiliated political groups due to health reasons.

BuzzFeed News reported Tuesday that Koch's brother, Charles Koch, announced the move in a memo to employees.

Charles Koch wrote that David Koch was hospitalized in October 2016, and that "these issues have not been resolved and his health has continued to deteriorate."

"As a result, he is unable to be involved in business and other organizational activities," Charles Koch said.

David Koch was diagnosed with prostate cancer 25 years ago. He donated millions to cancer research and medical groups.

However, the Kochs have become known largely for their massive political contributions to Republican candidates and libertarian-leaning causes.

The brothers did not support President Trump during the 2016 campaign, but have supported him on certain issues since he took office, such as the GOP tax cut bill.

The Koch network has been a staunch opponent of Trump's decision to implement steel and aluminum tariffs on Canada, Mexico and the European Union.

Three advocacy groups backed by the Kochs on Monday announced a multimillion-dollar campaign to push back against the tariffs. Freedom Partners, Americans for Prosperity and The LIBRE Initiative will take out ads, hold events and engage in lobbying as part of the effort.