Warren Buffett will step down as the chairman of Berkshire Hathaway effective immediately, the company announced Friday.

His son, Howard—a Berkshire director since 1993—will replace him as chairman. Warren Buffett will now serve as chairman emeritus of the company and remain a member of the board.

The move came a little more than nine months after Buffett retired as CEO of Berkshire and was replaced by Greg Abel. Buffett wrote in a letter to shareholders on Friday that the timing to step down as chairman was right as Abel had been “making the decisions that matter for some time” and had exceeded his expectations as head of the company.

“Greg runs the company; Howard will guard its culture and values—both worth more than anything on our balance sheet. Think of Howard as a policy the shareholders own and hope never to claim against,” Buffett wrote.

At the time of his resignation, Buffett was the controlling shareholder with a a 30% voting interest. Now 96, Buffett has said he wants give away all his Berkshire stock—a 13% stake worth more than $140 billion—by 2034.

“Serving as your chairman has been the privilege of a lifetime, and I have never taken your trust for granted. Father Time always wins,” Buffett wrote. “The company is in excellent hands, and I look forward to remaining a shareholder alongside you.”

Berkshire said Susan Decker, a board member since 2007, will continue to serve as lead independent director.

Berkshire’s Class A shares, which ended Thursday at $763,936, have risen 1.2% this year coming into Friday’s session but have underperformed the S&P 500.

Under Abel’s leadership, Berkshire has boosted stock repurchases but hasn’t made many major new investments. The company’s huge cash position totaled about $365 billion on June 30, down from around $380 billion on March 31.

“Warren’s impact on Berkshire and its owners is without parallel in the history of American business. The culture Warren built and the values he championed will remain at the heart of Berkshire, and Howard will be their guardian,” Abel wrote in a company statement Friday.