Theresa May entered No. 10 Downing St., on Wednesday as Britain's new prime minister, following a bittersweet exit by David Cameron that was tinged with humor and regret.

May stood in front of the iconic door of No. 10 with her husband, Philip, as the 13th prime minister of the queen's reign and the first woman to hold the job since fellow Conservative Margaret Thatcher served from 1979 to 1990.

May acknowledged that Britain faces a rocky road ahead as it undoes 43 years of EU ties and forges a new relationship with its neighbours

As we leave the European Union we will forge a bold new positive role for ourselves in the world and we will make Britain a country that works not for a privileged few, but for every one of us, May said.

May promised to fight for social justice in a speech that addressed hard-working families who have struggled during the years of instability since the 2008 financial crisis. Many of those people, fed up with remote politicians and bureaucrats, voted to leave the EU.

I was the future once, Cameron quipped as he left office. But that future now belongs to May, and it involves instability, uncertainty and tough wrangling over Britain's departure from the European Union.

Later, in a brief speech on Downing Street, the 49-year-old Cameron defended his government's legacy.

David Cameron with his wife Samantha and children leaving 10 Downing Street. Cameron announced his resignation after voters rejected his appeal to stay in the 28-nation bloc

Then, Cameron and his wife, Samantha, and his children, 12-year-old Nancy, 10-year-old Elwen and 5-year-old Florence left their home of six years and made the short drive to Buckingham Palace.