Tanzania's four main opposition parties on Tuesday named former prime minister Edward Lowassa - once seen as a leading contender for the ruling party nomination - as their joint presidential candidate ahead of October's general election.
The Chama Cha Mapinduzi (CCM) party of outgoing President Jakaya Kikwete has ruled Tanzania since independence in 1961. The opposition's nomination of Lowassa, who crossed party lines last week, could shake up the political landscape.
"I have come to join you for a reason, to remove CCM from power," Lowassa told cheering delegates after being named by the coalition, including CHADEMA - Tanzania's biggest opposition party - in Tanzania's commercial capital, Dar es Salaam.
On July 12, CCM instead nominated Works Minister John Magufuli, a long-serving cabinet minister from the gold-rich lake zone area, the east African state's biggest electoral bloc.
Tanzania has been one of Africa's most politically stable nations, spared of the sort of strife raging in other parts of the continent where some presidents have sought third terms despite constitutional restrictions.
Tanzania's next leader is expected to help develop the country's nascent hydrocarbons industry. Tanzania is estimated to have 53.2 trillion cubic feet (tcf) of gas reserves off its southern coast.
Lowassa, 61, had been seen as a frontrunner in CCM's presidential nomination race, and it caught many by surprise that he was not included in the short list of candidates.
There was speculation that past graft allegations could have hurt Lowassa among CCM leadership. The government was thrown into turmoil earlier this year after a graft scandal in the energy ministry led to the ouster of several top CCM officials, including the attorney general and energy minister.
Lowassa quit as premier in 2008 after a parliamentary investigation linked him to irregularities in a government contract for emergency power generation. Lowassa was never charged with a crime and he has denied wrongdoing.
The opposition CHADEMA party had previously named Lowassa in its 'List of Shame' of government leaders with corruption allegations, but has now rallied behind the ex-premier saying the allegations against him were never proven.