Bill Gates is stepping down from the boards of Microsoft and Berkshire Hathaway.

In a press release Friday, Microsoft announced that its 64-year-old co-founder was leaving its board to "dedicate more time to his philanthropic priorities."

"It's been a tremendous honor and privilege to have worked with and learned from Bill over the years," Microsoft CEO Satya Nadella said in a written statement. "Microsoft will continue to benefit from Bill's ongoing technical passion and advice to drive our products and services forward. I am grateful for Bill's friendship and look forward to continuing to work alongside him to realize our mission to empower every person and every organization on the planet to achieve more."

Gates will continue serving as technology adviser to Nadella and other Microsoft leaders, the company said.

Separately in an SEC filing, Berkshire Hathaway said former American Express CEO Kenneth Chenault would replace Gates, who has served on Berkshire's board since 2004.

Chenault simultaneously is leaving Facebook's board of directors, the company confirmed Friday. The 68-year-old has served on Facebook's board since 2018, after his retirement as chairman and CEO chairman and CEO of AMEX.

In a written statement posted on Facebook's website Friday, Chenault said serving on Berkshire Hathaway's board and working closely with his friend, Berkshire CEO Warren Buffett, is "a once-in-a-lifetime opportunity."

"I also believe good corporate governance entails limiting the number of board commitments for any director," Chenault said.

With an estimated net worth of over $100 billion, Gates is the second richest person in the world after Amazon's Jeff Bezos, according to the Bloomberg Billionaire Index. He has worked on global health, industrial development and education initiatives through the Bill and Melinda Gates Foundation since transitioning out of day-to-day duties at Microsoft in 2008.

Gates's role as chair of Microsoft's board ended in 2014. He plans to do more work to tackle climate change, according to the company.