On Wednesday, Warren Buffett resigned as a trustee of the Bill and Melinda Gates Foundation, one of the world’s greatest private philanthropic organisations, while also donating another $4.1 billion in Berkshire Hathaway shares to charity.

Since 2006, Buffett has made annual donations to five charitable foundations as part of a commitment to donate 99 percent of his net assets to charity. Buffett stated in a statement, “With today’s $4.1 billion dividend, I’m halfway there.”

He didn’t say why he was quitting the Gates Foundation board at this time, but he did say he supported the current CEO and the foundation’s strategy. After 27 years of marriage, Bill Gates and his wife Melinda, co-founders of the foundation, filed for divorce in May, but have promised to continue their charitable work together.

The 21-year-old foundation has grown to be one of the most powerful and influential organisations in global public health, having spent more than $50 billion over the last two decades to apply a commercial approach to tackling poverty and illness.

Buffett revealed last year that he had donated more than $2 billion in Berkshire shares to the Gates Foundation as part of his previously declared ambitions to give away his entire wealth before he died. “I’ve been a trustee of only one beneficiary of my donations, the Bill and Melinda Gates Foundation, for years – an inactive trustee at that. “I am quitting from that position, as I have from all other company boards save Berkshire Hathaway’s,” Buffett stated.