Thomas Cook Group Plc said Chief Executive Officer Harriet Green, the woman credited with restoring the fortunes of the 173-year-old travel company, is stepping down immediately. The shares fell as much as 24 percent on the news.

In a surprise move, the company said she would be replaced by Chief Operating Officer Peter Frankhauser, a year after he was promoted to that position.

Chairman Frank Meysman said on a conference call with journalists today that the change in leadership marks a shift in direction from restructuring towards implementation of the company’s strategy. Frankhauser has more experience of the travel market, he added.

“The strategy is there and it will not change, it is now a matter of executing that strategy,” Meysman said. “Knowledge of the market is more important,” he said, adding that, after 13 years at Thomas Cook, the new CEO is a “travel experience expert.”

Before becoming COO, Frankhauser was in charge of Thomas Cook’s U.K. and continental European operations. Green had held the CEO role for two years, Thomas Cook said in a statement today.

The company’s loss after tax was 115 million pounds ($180.7 million) for the year ended Sept. 30, compared with a loss of 213 million pounds a year earlier, Thomas Cook said in a separate statement. Sales fell almost 8 percent to 8.5 billion pounds.

The shares were down 23 percent at 106 pence as of 8:34 a.m. in London.

To contact the reporter on this story: Kari Lundgren in London at klundgren2@bloomberg.net. To contact the editors responsible for this story: Benedikt Kammel at bkammel@bloomberg.net.

Photo Credit: New branding introduced last fall. Thomas Cook