Former British Prime Minister Boris Johnson says he will not run to lead the Conservative Party, ending intense speculation about a comeback.

Johnson, who was ousted in July amid ethics scandals, was widely expected to run to replace Liz Truss, who quit last week.

He has spent the weekend trying to gain support from fellow MPs, and said he had amassed more than 100 votes, the threshold to run.

But he was far behind former Treasury chief Rishi Sunak in support. Johnson said he had concluded that “you can’t govern effectively unless you have a united party in Parliament”.

Sunak garnered the public support of over 100 Tory MPs to forge ahead of his two main rivals: Johnson and ex-Cabinet minister Penny Mordaunt.

The Conservative Party hastily ordered a contest that aims to finalise nominations Monday and install a new prime minister — its third this year — within a week.

Sunak, 42, was runner-up after Truss in this summer’s Tory leadership race to replace Johnson after he was forced out by a string of ethics scandals.

Sunak has the backing of at least 124 Conservative MPs, according to unofficial tallies compiled by British news organisations. That’s well ahead of the 100 nominations required to qualify.

“There will be integrity, professionalism and accountability at every level of the government I lead and I will work day in and day out to get the job done,” Sunak said in a statement.

Truss quit Thursday after a turbulent 45 days, conceding that she could not deliver on her botched tax-cutting economic package, which she was forced to abandon after it sparked fury within her party and weeks of turmoil in financial markets.

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Sunak, who was Treasury chief from 2020 until this summer, steered Britain’s slumping economy through the coronavirus pandemic. He quit in July in protest of Johnson’s leadership.

In the summer contest to replace Johnson, Sunak called promises by Truss and other rivals to immediately slash taxes reckless “fairy tales” and argued that climbing inflation must be controlled first.