Shares of Fiat Chrysler Automobiles and Ferrari dropped Monday following the abrupt departure of CEO Sergio Marchionne, who fell seriously ill following shoulder surgery.

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Fiat Chrysler announced on Saturday that Mike Manley, head of its Jeep and Ram brands, would take over as CEO, adding that Marchionne will be unable to return to work. At Ferrari, longtime Philip Morris executive Louis Camilleri will run the sports car maker, while John Elkann will serve as its chairman. Elkann is the current chairman of Fiat Chrysler and a member of the Agnelli family that controls the automaker.

Fiat Chrysler also said Monday the head of its business in Europe, the Middle East and Africa, Alfredo Altavilla, had resigned. Manley will oversee the business on an interim basis.

Shares of Fiat Chrysler were about 2% lower in afternoon trading. Ferrari was down 2.5%.

The sudden C-suite transition worried investors who had expected Marchionne, 66, to remain involved with Fiat Chrysler in some form following a planned departure in 2019. Marchionne is considered a key figure in the automotive industry and the histories of Fiat and Chrysler. He oversaw the transformative merger of the two car manufacturers and was instrumental in their resurgence, including Jeep’s global expansion.

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