Thomas Cook's share price tumbled by more than a fifth on Wednesday after the British travel group announced the exit of chief executive Harriet Green.
Green has left with immediate effect and has been replaced by chief operating officer Peter Fankhauser, the group said in a statement to the London Stock Exchange.
In reaction, shares tumbled 20.09 percent to 110.2 pence in morning deals on London's second-tier FTSE 250 index, which was flat at 15,831.06 points.
Shares were also hit as Thomas Cook warned in a separate earnings statement that it expects growth this year to be at a more moderate pace due to the tougher trading environment.
Green said her work at the once-troubled company was done, after returning it to a sound financial footing during her two years at the helm.
"I always said that I would move on to another company with fresh challenges once my work was complete. That time is now," she said Wednesday.
"I wish all of the team at this re-energised company continued success, as they move to the next phase of the company's development."