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June 17 (Reuters) - Exchange operator CME Group CME.O on Wednesday named insider Lynne Fitzpatrick its next CEO, to succeed longtime chief Terry Duffy, who will become executive chairman.

Duffy, who was appointed chairman in 2002 and has led CME for more than 25 years, will step down on March 1. Shares of the exchange operator were down 4% in premarket trading.

Fitzpatrick, currently CME's president and chief financial officer, will also join the company's board when she takes over as CEO, CME said.