The Prime Minister's brother, Jo Johnson, has announced he is leaving politics, saying he had been "torn" between the national interest and family.
The Tory MP and universities minister announced on Twitter he was resigning from the government, ending his announcement with the words "over and out".
He wrote: "It's been an honour to represent Orpington for 9 years & to serve as a minister under three PMs.
"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."
As a senior minister, Mr Johnson attended meetings of his brother's Cabinet.
Following his announcement, a Number 10 spokesman said Jo Johnson had been “a brilliant, talented minister and a fantastic MP”, and that the Prime Minister “as both a politician and brother understands this will not have been an easy matter for Jo”.
Jo Johnson is pro-European and has previously called for a second referendum, a position that put him at odds with the Prime Minister, who has vowed to leave the EU on October 31 with or without a Brexit deal.
Reacting to the news, former cabinet minister David Gauke, who was one of 21 MPs ousted from the Conservative Party this week, tweeted: "Lots of MPs have had to wrestle with conflicting loyalties in recent weeks. None more so than Jo.
"This is a big loss to Parliament, the Government and the Conservative Party."
And Labour MP and shadow home secretary, Diane Abbott, said: "If his own brother has no confidence in Boris Johnson, why should anybody else?".