New Delhi, July 15 -- OMAHA - Twenty years after declaring his gift to the Gates Foundation "irrevocable," Warren Buffett on Tuesday excluded it from his annual donation of Berkshire Hathaway shares, ending a philanthropic partnership that had channeled billions into the world's largest private charitable organization since 2006.

Buffett transferred 12 million Class B shares of Berkshire Hathaway (BRK.B), worth roughly $6 billion at current prices, to four foundations managed by his children. The Gates Foundation - which had received a portion of Buffett's Berkshire shares every year since the original pledge - received nothing.

CNBC, which first reported the development, said Tuesday's omission marks the first time since 2006 that Buff...