Boris Johnson becomes UK prime minister

Boris Johnson arrives at Buckingham Palace in London for an audience with Queen Elizabeth II, in London, Britain July 24, 2019.

Britain's Prime Minister Boris Johnson is welcomed in 10 Downing Street by staff after meeting Britain's Queen Elizabeth II and accepting her invitation to become Prime Minister and form a new government, in London, Britain July 24, 2019. Stefan Rousseau/Pool via REUTERS

Theresa May speaks on her last day in office as Britain's Prime Minister, at the House of Commons in London, Britain July 24, 2019. ©UK Parliament/Jessica Taylor/Handout via REUTERS

Theresa May is seen on her last day in office as Britain's Prime Minister, at the House of Commons in London, Britain July 24, 2019. ©UK Parliament/Roger Harris/Handout via REUTERS

Boris Johnson is driven into Buckingham Palace, In London, Britain July 24, 2019.

Protestor wearing a mask depicting Boris Johnson is seen in front of Buckingham Palace, in London, Britain July 24, 2019

Theresa May arrives to deliver a speech on her last day in office as Britain's Prime Minister, outside Downing Street, in London, Britain July 24, 2019.

Boris Johnson's girlfriend, Carrie Symonds, is seen outside Downing Street in London, Britain July 24, 2019.

Boris Johnson's girlfriend, Carrie Symonds, is seen outside Downing Street in London, Britain July 24, 2019.

People hold placards as they demonstrate against newly appointed British Prime Minister Boris Johnson outside Downing Street in London, Britain July 24, 2019.

Theresa May and her husband Philip wave outside Downing Street, on her last day in office as Britain's Prime Minister, in London, Britain July 24, 2019.

Britain's Prime Minister Boris Johnson is welcomed in 10 Downing Street by staff after meeting Britain's Queen Elizabeth II and accepting her invitation to become Prime Minister and form a new government, in London, Britain July 24, 2019. Stefan Rousseau/Pool via REUTERS