John McCallister, the deputy leader of NI21, has revealed his reasons for resigning from the troubled political party – saying Basil McCrea's ego was a problem.
In an exclusive interview with the Belfast Telegraph, the MLA said "disillusionment" with his party leader led him to resign from the organisation.
He claimed that he and Mr McCrea were initially supposed to have a joint leadership, but "Basil moved away from that".
"Basil's ego was never going to let me be party leader," he said.
Mr McCallister said he will remain in politics as an independent unionist MLA for South Down.
Northern Ireland's newest political party has been on the brink of collapse since a public falling-out between Mr McCallister and party leader Mr McCrea after the deputy instigated an external investigation into allegations of inappropriate sexual activity against his former colleague. Mr McCrea strongly denies the allegations.
Speaking about his reasons for standing down, Mr McCallister said his position as deputy leader, chief whip and member of NI21 had become untenable after the investigation by mediation firm Carecall was halted by the party.
The allegations have now been referred to the Assembly's Commissioner for Standards.
Mr McCallister said that had Mr McCrea stepped down as party leader while the investigation was ongoing, he may have remained.
He added: "With everything that has been going on within the party over the last few months, I have felt in a very difficult position.
"I felt my time shouldn't be spent fighting over issues within NI21 whenever I should be fighting for the issues that matter to the people of Northern Ireland."
Mr McCallister said he intended to stay an independent unionist MLA "to focus on continuing to be a good, active constituency representative".
He added that he would "still be out presenting the values and agenda that I wrote for NI21 about wanting to see a normal society, about wanting to see a Government opposition, wanting to see a tolerant, inclusive, pluralist pro- Union voice in the Assembly".
Mr McCallister and Mr McCrea left the Ulster Unionist Party to set up NI21, but the party descended into chaos after its executive proposed dropping its unionist designation at Stormont two days before voters went to the polls, a proposal that angered Mr McCallister.
However, he revealed that he was already deeply disillusioned with the party at that time because of the "dysfunctional" way it was being run.
"There were things like the very late selection of a European candidate (Tina McKenzie) , the very late selection of candidates for council and the late announcement of those candidates.
"There was an executive that wasn't keeping minutes or doing a proper agenda for meetings. There was huge disillusionment," he said.