LONDON — Xavier Rolet, the chief executive of the London Stock Exchange Group, and Carsten Kengeter, his counterpart at Deutsche Börse, were preparing a year ago to combine two of Europe’s biggest stock exchange operators into a regional behemoth.
The merger was ultimately blocked by regulators, and now both men are to leave their positions under a cloud.
Mr. Rolet, who has led the London stock market operator since 2009, said on Wednesday that he would step down immediately, following a public fight between the exchange and a major investor over his planned departure at the end of next year.
During his tenure, the London Stock Exchange Group expanded its size and scope through a series of mergers. Its shares now trade at more than five times their value when Mr. Rolet took the top job in May 2009, in the midst of the financial crisis, and more than twice the pre-crisis high. Shares of the exchange operator were down about 2 percent on Wednesday.