JOHANNESBURG, July 23 (Reuters) – Shares in South Africa’s Telkom slumped on Friday after the company announced that CEO Sipho Maseko would step down at the end of June next year after more than eight years at the helm of the country’s third-biggest telecoms provider .

Maseko, who is also the executive director of the group, had been brought to Telkom in 2013, when the company was facing declining fixed-line voice revenue, bulk of its business back then, as consumers were moving to mobile and data services.

Under Maseko’s leadership, Telkom said it had assembled an array of mobile, IT, wholesale infrastructure businesses and along with a mast and tower portfolio.

The mobile business grew to become the third largest in South Africa with more than 15 million customers, generating 20 billion rand ($1.35 billion ) of revenue, Telkom said.

“I feel now is the right time for me to step aside and make way for a new leader who will take Telkom to even greater heights,” Maseko said in a separate statement.

Telkom also said it is in the process of finding Maseko’s successor who would be announced “in the not too distant future.”

Uncertainty generated by the announcement unnerved investors.

By 0922 GMT, shares in Telkom had declined by 6.10% to a two-month low. Meantime, the broader all-share index was up 1.16%.

Read more: South African telecom operator Telkom moves into financial services

Peter Takaendesa, head of equities at Mergence Investment Managers, said Maseko’s departure raised some questions.

“He is credited for the turnaround strategy and obviously the market was expecting him to still be there for a while…because there is one piece of the puzzle that hasn’t been put in place which is value unlock,” said Takaendesa.

Telkom has said it was close to finding investors for its mast and tower business, which it reckons is undervalued since it is trapped in the group structure.

($1 = 14.7626 rand)

(Reporting by Nqobile Dludla and Promit Mukherjee; editing by Uttaresh.V & Simon Cameron-Moore)