LONDON, (AA): The contest to select Britain’s next prime minister took a dramatic and unexpected turn Thursday when Boris Johnson withdrew from a race dominated by last week’s Brexit decision.

The former London mayor and one-time chat show host is a popular personality in the U.K. His decision to endorse the Leave side in his country’s EU membership referendum was seen as a star signing and a critical factor in securing last week’s narrow vote for Brexit.

As he appeared in front of television cameras at a central London hotel Thursday morning, Johnson had been expected to launch his heavily-trailed candidacy for leadership of Britain’s governing Conservative Party.

Instead, Johnson listed a series of priorities that faces the person who succeeds Prime Minister David Cameron and added: “That is the agenda for the next prime minister of this country.”

– Shock announcement

“Well, I must tell you, my friends, you who have waited faithfully for the punch line of this speech, that having consulted colleagues and in view of the circumstances in parliament, I have concluded that person cannot be me.”

It was a decision taken so quickly than even the Conservative lawmakers in the audience who had already endorsed him did not know it was coming.

Although not named in Johnson’s speech, the reason for the withdrawal was Justice Secretary Michael Gove, a fellow Brexit campaigner and erstwhile ally, who had that morning declared he was running for the job himself.

“I respect and admire all the candidates running for the leadership,” Gove said in a statement released just before 8 a.m. (0700 GMT) that morning.

“In particular, I wanted to help build a team behind Boris Johnson so that a politician who argued for leaving the European Union could lead us to a better future.

“But I have come, reluctantly, to the conclusion that Boris cannot provide the leadership or build the team for the task ahead.”

– ‘A Ph.D. in ruthlessness’

The impact on the former London mayor’s leadership hopes was devastating. The two men had built a close relationship during the EU referendum campaign and Gove was widely assumed to have been offered a senior ministerial role by Johnson in exchange for his support.

But, as Gove told the BBC later Thursday afternoon, he came reluctantly and firmly to the conclusion that while Boris has great attributes he was not capable of uniting that team and leading the party and the country in the way that I would have hoped.”

He said Britain’s next prime minister should be someone who had campaigned to leave the EU and that, as a consequence, the task of running for the top job fell to him.

“The Tory [Conservative] party has proved yet again it has [a] Ph.D. in ruthlessness,” Guardian journalist Martin Kettle tweeted shortly after Johnson’s withdrawal was confirmed. Other reporters compared the episode to the assassination of Roman emperor Julius Caesar.

– New frontrunner

Johnson’s withdrawal meant the clear favorite in the campaign to succeed Cameron as prime minister became Theresa May, the home secretary, who had gathered the support of more than 60 Conservative lawmakers by Thursday afternoon.

May was a supporter of Britain’s continued EU membership, albeit a low-key one, but she could not avoid referring to the referendum result as she announced her candidacy Thursday morning, shortly before Johnson spoke.

She told her audience: “Brexit means Brexit. The campaign was fought, the vote was held, turnout was high, and the public gave their verdict. There must be no attempts to remain inside the EU, no attempts to rejoin it through the backdoor, and no second referendum.

“The country voted to leave the European Union, and it is the duty of the government and parliament to make sure we do just that.”

May said her six years as home secretary gave her the qualities needed to face the challenge of taking Britain out of the European Union.

“Following last week’s referendum, our country needs strong leadership to steer us through this period of economic and political uncertainty and to negotiate the best possible terms as we leave the EU,” she said.

“We need leadership that can unite our party and our country.”

– Five contenders

In addition to May and Gove, Energy Minister Andrea Leadsom and former Defense Secretary Liam Fox — both prominent supporters of Britain’s EU exit, or Brexit — and Work and Pensions Secretary Stephen Crabb, who supported staying in the EU, are also seeking to take over from Cameron in early September.

Under party election rules, the field of candidates will be reduced to two in a vote among the party’s lawmakers. The first vote will take place next Tuesday, July 5.

The remaining two candidates will then spend the summer canvassing Conservative party members, who will vote to choose between them. The winner will be declared on Sept. 9.

[Photo: Boris Johnson, the favored candidate to succeed David Cameron, drops out after an erstwhile ally decides to oppose him Photographer: Neill Hall/AA]