Veteran Cameroonian politician John Fru Ndi has split from an opposition coalition to stand as a candidate in next month's presidential election.
Mr Fru Ndi has strong support in English-speaking areas
His announcement follows the nomination by a 10-party opposition coalition of Adamou Ndam Njoya as its candidate.
Mr Fru Ndi said that Mr Njoya had not been selected democratically.
He also accused President Paul Biya, who is bidding for a fourth term in office, of trying ensure victory by dividing the opposition.
"I'd be very surprised if the problems we are having in the coalition are not masterminded by him [President Biya]," Mr Fru Ndi told the BBC's Network Africa programme.
He said he was running for as a presidential candidate on 11 October because his Social Democratic Front party had more parliamentarians and mayors than Mr Njoya's Cameroon Democratic Union.
Mr Fru Ndi, who has strong backing in English-speaking regions, claims he won rigged elections in 1992.
The split is a disaster for opposition hopes of unseating Mr Biya, says the BBC's Randy Azeng in Bamenda.
Mr Njoya is a francophone politician and a former minister of education.