Chipotle Mexican Grill founder Steve Ells has stepped down from the chain's board and relinquished his title of executive chairman after current CEO Brian Niccol was named chairman.

"Brian has proven that he is absolutely the right person to lead Chipotle forward and I've never been more confident about the future of this great company," Ells said in a statement. "I am especially grateful to the employees and our valued customers over the last 27 years who helped make Chipotle the unmatched brand in fast casual dining it is today."

Ells served as chief executive of Chipotle until November 2017. He founded the burrito chain in 1993, opening the first location near the University of Denver campus and growing it to more than 2,000 locations. He stepped down as CEO as the company struggled to rebound from its food safety woes, which plagued Chipotle for two years.

Niccol became Chipotle's CEO in early March. Under his leadership, the restaurant has seen its sales bounce back and its stock price reach all-time highs.

Chipotle also announced Friday that Matthew Paull and Paul Cappuccio will not stand for re-election to the board at the company's annual shareholder meeting on May 19. After the meeting, Chipotle will have seven directors on its board, six of whom are independent.

Paull previously served on Chipotle's board when McDonald's owned a majority stake in the chain. The former McDonald's CFO was reappointed to the board in December 2016 as part of the chain's agreement with Bill Ackman's Pershing Square Capital Management. Paull serves on the advisory board for the hedge fund, which has been trimming its investment in Chipotle. Pershing's other appointee Ali Namvar will remain on the board.

Cappuccio, who is general counsel of Time Warner, has also served on the board since December 2016.

Chipotle's stock, which has a market value of $19.6 billion, was down more than 2% in morning trading, against a backdrop of widespread selling. In the last 12 months, shares are up 15%.