Henry Bolton has been ousted as Ukip leader after party members backed a motion of no confidence in him.
At a crisis meeting in Birmingham, activists voted by 867 to 500 to express their lack of faith in his ability to lead the party.
The move now leaves the party facing a further period of uncertainty, with Mr Bolton forced out after only being elected in September last year.
Mr Bolton had attempted to cling on to the leadership despite a no confidence vote by the ruling national executive committee (NEC) and a revolt by several senior figures in the party in protest at his relationship with model Jo Marney.
Mr Bolton said he still has “strong affections” for his former girlfriend who sent offensive messages about Meghan Markle, and compared the scrutiny of his private life to that faced by Diana, Princess of Wales.
Ukip will face a fresh leadership election within 90 days after Mr Bolton lost the no confidence motion.
Outgoing chairman Paul Oakden said: “Henry Bolton has been removed by the democratic decision of the membership”.
Gerard Batten will take over as Ukip’s interim leader, the party announced.
Speculation is mounting that Mr Bolton’s exit could pave the way for the return of former leader Nigel Farage.
Senior Ukip figure Suzanne Evans told the Press Association ahead of the vote that it was “crunch time” for the party and Mr Farage should again take the helm.
The pro-Brexit party has lurched from crisis to crisis since Mr Farage relinquished power following the 2016 referendum, with a succession of leading party figures failing to keep a grip on the leadership.
Mr Bolton earlier said he thought “it’s going to be very difficult for the party to survive” another round of leadership turmoil.
He had also suggested he would not rule out running for the top job again in future.
The cash-strapped party faces a separate series of challenges, including the prospect of a hefty legal bill over a defamation action brought by Rotherham’s three Labour MPs against MEP Jane Collins.