Jo Johnson, the brother of British Prime Minister Boris Johnson, resigned abruptly Thursday from the British government, citing “unresolvable tension” between family loyalty and the “national interest” as political turmoil surrounds Britain’s attempt to leave the European Union.

“It’s been an honour to represent Orpington for 9 years & to serve as a minister under three PMs,” Jo Johnson wrote on Twitter. “In recent weeks I’ve been torn between family loyalty and the national interest — it’s an unresolvable tension & time for others to take on my roles as MP & Minister. #overandout

Johnson — a member of Britain’s Conservative Party, known informally as the Tories — served as a member of Parliament for Orpington, a district on the southeastern outskirts of London, and was a member of his brother’s cabinet overseeing business and education.

His resignation is just the latest bit of bad news for his brother, who has promised to deliver Brexit by the end of October. The brothers’ ideological disagreements have been well documented — Jo Johnson voted against Brexit in 2016 and has campaigned for a second referendum — but Jo Johnson’s resignation was unexpected.

As The Washington Post reported Wednesday, Boris Johnson, after just six weeks on the job as prime minister, has lost his governing majority, exiled some of his party’s most honored members and been slapped down by lawmakers three times in 24 hours. Jo Johnson voted Wednesday to back his brother’s call for an early election, but he again cast his ballot against leaving the E.U.

A spokesman for the prime minister said Thursday that Jo Johnson had been “a brilliant, talented minister and a fantastic MP” and that Boris Johnson “as both a politician and brother understands this will not have been an easy matter for Jo."

The British House of Commons passed a bill Sept. 4 seeking to avert a no-deal Brexit on Oct. 31 in another setback for prime minister Boris Johnson’s plan. (Reuters)

Boris Johnson has been pushing for an early general election for all 650 seats in the House of Commons in hopes that the results of an Oct. 15 vote would aid him in a Brexit-related meeting two days later. He recently called Labour Party leader Jeremy Corbyn’s refusal to back an early election “a cowardly insult to democracy.” Voters, Johnson said, should be able to choose through their parliamentary votes between him and Corbyn, who he said would seek “more delay, more dither."

The question of whether or when Britain will separate from the E.U. has roiled the nation for years and left citizens frustrated with the seemingly endless tumult. This week alone, protesters marched, and legislators abandoned or were kicked out of their parties.

Although the Johnson brothers have clashed over Brexit, both previously resigned from the cabinet of then-Prime Minister Theresa May. Boris Johnson asserted May was surrendering to the E.U.'s Brussels headquarters in Brexit negotiations, while Jo Johnson said May was asking the country to choose between subservience to the E.U. or the “chaos” of a “no-deal Brexit,” in which Britain would leave the E.U. without reaching an agreement with its other members.

Unlike his brother, Jo Johnson in November proposed asking the British people again if they still supported leaving the continental trading bloc.

“It is imperative that we now go back to the people and check that they are content to proceed on this extraordinary basis,” he said at the time.

Rachel Johnson, Boris and Jo’s sister, said Thursday that “the family avoids the topic of Brexit especially at meals as we don’t want to gang up on the PM!”

Members of the Labour Party said Thursday that Jo Johnson’s resignation underscored his brother’s ineffectiveness as a leader.

“Boris Johnson poses such a threat that even his own brother doesn’t trust him,” Angela Rayner, a member of Parliament and Labour’s shadow education secretary, said in a statement. “We have now had four higher education ministers in two years — just the latest sign of the chaos that the Tories have caused to education and the threat that a disastrous No Deal Brexit poses to our colleges and universities.”

Ian Murray, a Labour member of Parliament, wrote on Twitter: “Even Boris Johnson’s brother knows that he can’t be trusted to make decisions in the national interest. This is devastating from Jo Johnson.”

David Gauke, a Conservative Party member of Parliament who served in May’s cabinet, called Johnson’s resignation a “big loss.”

“Lots of MPs have had to wrestle with conflicting loyalties in recent weeks. None more so than Jo,” Gauke wrote. “This is a big loss to Parliament, the Government and the Conservative Party.”

Sadiq Khan, the mayor of London and a member of the Labour Party, said he was sorry to see Johnson leave government.

“This is a big loss to London and Parliament,” Khan wrote on Twitter. “Working with @JoJohnsonUK when he was the Minister for London meant putting aside party political differences in the best interests of Londoners.”

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