In a sign of the turmoil currently engulfing McDonald's ( MCD), investors bid up the fast-food giant's shares Thursday on news the company's CEO, Jack Greenberg, was retiring. They've since settled back, possibly as investors realize his successor is also a longtime company insider.

The fast-food giant announced Thursday the retirement of chairman and chief executive Greenberg after 21 years with the company. During five years at the helm, Greenberg presided over a massive expansion of the hamburger chain, but his departure comes with the shares near their 52-week low after several years of weakening sales.

"In every company's history, there is a time when it is appropriate to pass the baton and give a new management team the opportunity to lead, and that time has come at McDonald's," Greenberg said.

McDonald's shares, which traded as low as $17.78 earlier Thursday following a bombing at one of its Indonesian restaurants, shot up to $19.19 after headlines about Greenberg's departure were published. They were recently at $18.50, however.

Greenberg's successor is McDonald's veteran Jim Cantalupo, who returns after a brief absence. Cantalupo was last vice chairman and president of the company after being hired as a controller in 1974. In 1987, he was appointed president of McDonald's International, and eventually chairman and CEO of McDonald's International, where he earned praise for engineering the international business success of McDonald's.

Charlie Bell, currently president of McDonald's Europe, was appointed president and chief operating officer of the parent, and Jim Skinner was named vice chairman. Bell was also named a director. Both Bell and Skinner will report directly to Cantalupo.

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