Chipotle shares fell as much as 10% in premarket trading on Tuesday as the company announced that CEO Brian Niccol would leave his post on August 31 to become CEO of Starbucks.

Niccol took over as CEO of Chipotle in March 2018. Since he took over, Chipotle’s stock price has increased by more than 770%.

Chipotle’s board of directors appointed Chief Operating Officer Scott Boatwright as interim CEO. He has been with the company since 2017. The board also announced that Chief Financial Officer Jack Hartung, who had announced his plans to retire, will stay with the company indefinitely to assist with the transition.

“We saw in Brian someone who, quite frankly, has been through it all – all kinds of market environments, all kinds of cycles,” Mellody Hobson, who was chief executive of Starbucks but resigned to become lead independent director as part of the changes on Tuesday, said on CNBC’s Squawk Box. “When I spoke to him, he said, ‘I know what to do.'”

Chipotle saw strong sales growth and customer traffic at its existing stores, while other restaurants reported a decline in customer spending.

Chipotle reported second-quarter earnings in July that beat analyst estimates and reported revenue of $2.97 billion. Net sales rose 18.2 percent in the quarter, with store sales rising 11.1 percent.

Niccol helped lead Chipotle through a food scandal and oversaw the restaurant chain during the pandemic.

Before taking the helm at Chipotle, Niccol was CEO of Yum Brands’ Taco Bell.

Analyst Mark Kalinowski, CEO of Kalinowski Equity Research, was cautious about the CEO change.

“While this is viewed as bad for Chipotle in the short term, Mr. Niccol was CEO there for over six years, so the opportunity to bring some new ideas to this highly respected company may not be the worst thing in the world in the long run,” Kalinowski wrote in a statement on Tuesday.

— CNBC’s Amelia Lucas contributed to this report.