EE said Olaf Swantee will step down from his position as CEO after BT has completed its proposed deal to buy the UK-based mobile operator.
In a statement, EE said Marc Allera would take on the CEO role once the mobile operator has become a "new line of business" within the BT group. Allera is currently chief commercial officer at EE and has been with the company for four years.
Swantee said he had taken "the enormously difficult decision" to step down from his role as CEO to pursue new opportunities.
"I am immensely proud of the past four and a half years, creating, launching and growing EE to the exciting business it is today," Swantee said. "To leave EE is probably the hardest decision of my career, but I feel the time is right for me to handover for the next exciting chapter of EE's incredible journey."
It is not yet clear what Swantee will do next. He has certainly made his mark at EE, which became the first company to launch mobile services in the UK and was on track to reach 14 million 4G customers by the end of 2015.
Thomas Dannenfeldt, EE chairman and CFO of Deutsche Telekom, said EE had "delivered on every level" under Swantee's leadership.
"Based on a strategy of network and service supremacy, EE has shown a tremendously successful market and financial performance over a number of years. Marc has already greatly contributed to this success in the past and I wish him the best of luck in his new role."
BT received provisional clearance last October to acquire EE, after the UK Competition and Markets Authority (CMA) decided that the move would not substantially lessen competition in any market in the UK. The final report from the CMA is due by Jan. 18, 2016.
The provisional approval is an important step in BT's plan to create the UK's biggest converged provider of fixed and mobile telecoms services and follows the general trend towards consolidation in Europe. The former incumbent agreed in February 2015 to buy EE from existing owners Orange and Deutsche Telekom for £12.5 billion (€16.9 billion/$18.5 billion).
- see the EE announcement
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