Billionaire investor Warren Buffett said on Wednesday he was resigning from his position as trustee of the Bill and Melinda Gates Foundation (BMG), one of the world’s largest private charitable organizations.

“For years I have been a trustee – an inactive trustee at that – of only one recipient of my funds, the Bill and Melinda Gates Foundation. I am now resigning from that post, just as I have done at all corporate boards other than Berkshire’s,” Buffett said in a statement.

Bill Gates and his wife Melinda, co-founders of the foundation, filed for divorce in May after 27 years of marriage but pledged to continue their philanthropic work together.

The 21-year-old foundation has become one of the most powerful and influential forces in global public health, spending more than $50 billion over the past two decades to bring a business approach to combating poverty and disease.

Last year, Buffett reported donating more than $2 billion of stock in his investment vehicle, Berkshire Hathaway Inc, to the Gates Foundation as part of previously announced plans to give away his entire fortune before his death.

The 90-year-old also said he was pledging $4.1 billion to philanthropy.