U.K. Treasury chief Sajid Javid unexpectedly resigned on Thursday, in a shocking move after British Prime Minister Boris Johnson tried to use a reshuffle of his cabinet to get rid of some of Javid's aides.

Javid had been widely expected to keep his job – the second most powerful in the government – as Johnson fired certain Cabinet members, promoting more junior ministers to top jobs. The former Treasury chief, one of the strongest candidates in 2019 Conservative leadership contest, smiled as he entered the prime minister's 10 Downing St. office on Thursday morning to meet Johnson. However, a spokesman confirmed soon after that Javid had quit, becoming the shortest-serving chancellor of the exchequer since 1970. The government announced that he would be replaced by Rishi Sunak, previously a deputy to Javid at the Treasury. His resignation follows reports of clashes with Johnson's powerful adviser, Dominic Cummings.

Earlier, Johnson sacked his Northern Ireland minister despite his role in restoring devolved government to Belfast after a three-year suspension last month. Business Secretary Andrea Leadsom, Environment Secretary Theresa Villiers and Attorney General Geoffrey Cox were also shown the door. But Foreign Minister Dominic Raab and Michael Gove, Johnson's de factor deputy, are staying.

Johnson held off from carrying out a cabinet reshuffle immediately after his December victory, choosing to wait until Britain had left the EU. After years of political turmoil over Brexit, he claims to want to focus this year on domestic issues, including investments in police, healthcare and infrastructure.