Pro-immigration billionaire David Koch is reportedly stepping down from Koch Industries and other political networks due to health concerns.

In a company-wide memo, Charles Koch praised his brother David’s “guidance and loyalty.”

“Due to health reasons, David Koch will be resigning from the board of Americans for Prosperity Foundation,” Mark Holden, co-chairman of Seminar Network, said in a statement.

“We greatly appreciate his vital role on the board and all that he has done to help us build a strong foundation for our future success. We wish him and his family well.”

“Koch was diagnosed with prostate cancer more than two decades ago. Over the years, he and his family foundation, along with other recipients of Koch philanthropic support, have donated millions to battling cancer and several other causes. He is a board member of the Prostate Cancer Foundation,” CNBC reports.

The Koch brothers have long been controversial names in politics — first as boogeymen to the left, for their support of the Tea Party movement during the Obama administration, and now turning on populist conservatives with advocacy of globalist trade and immigration policies.

The LIBRE Initiatives, a Koch-backed group, is spending a seven-figure sum to send out mailers thanking pro-open borders Democrats ahead of the 2018 midterm elections.

The Koch-funded mailers praise Rep. Raul Ruiz (D-CA), Rep. Pete Aguilar (D-CA), Sen. Chris Coons (D-DE), Rep. Ben Ray Luján (D-NM), and Rep. Michelle Lujan Grisham (D-NM) for pushing amnesty for illegal immigrants.

On Monday, three Koch-backed groups — Freedom Partners, Americans for Prosperity, and LIBRE — announced a multi-million dollar ad and lobbying campaign to blunt the Trump administration’s efforts to slap tariffs on China, Canada, and the European Union.

“The Trump administration has taken some incredibly positive steps for the American economy, but tariffs will undercut that progress and needlessly hamstring our full economic potential,” Tim Phillips, Americans for Prosperity president, said in a statement.