Liz Truss on Tuesday officially became Britain's new prime minister, at an audience with head of state Queen Elizabeth II.
"The queen received in audience the right honourable Elizabeth Truss MP today and requested her to form a new administration," Buckingham Palace said in a statement.
"Ms Truss accepted Her Majesty's offer and kissed hands upon her appointment as prime minister.
The former foreign secretary is the 15th prime minister of the monarch's 70-year reign.
The symbolic ceremony took place at the sovereign's Balmoral retreat in the Scottish Highlands, as the Queen, 96, was deemed unfit to return to London due to ill health.
This came shortly after Boris Johnson handed the Queen his resignation in a separate ceremony.
Johnson, whose tenure was dominated by Brexit and Covid and cut short by a succession of scandals, earlier promised Truss his unswerving support as he made a farewell speech in Downing Street.
"I will be supporting Liz Truss and the new government every step of the way," he said, before leaving for Balmoral to cheers and applause from supporters.
He urged the Tories to put aside their ideological differences to tackle the energy crisis.
Truss, who was announced winner of an internal vote of Conservative party members on Monday, is expected to make her first speech as prime minister outside 10 Downing Street at about 4:00 pm (1500 GMT) on Tuesday.
Women in key cabinet posts
In terms of appointments, Business Secretary Kwasi Kwarteng is expected to become finance minister, with Attorney General Suella Braverman moved to the tricky brief of home secretary, and James Cleverly to foreign affairs.
If confirmed, it would mean there would be no white men in any of Britain's four main ministerial posts for the first time ever.
The contrast to her beaten leadership rival Rishi Sunak's more cautious approach has opened another rift in the Conservative party that was already divided by Johnson's departure.
The incoming prime minister faces a daunting to-do list, with the UK in the grip of its worst economic crisis in decades, with double-digit inflation and sky-rocketing gas and electricity bills.
The appointments are due to be finalised before she hosts her first cabinet meeting and faces questions in parliament on Wednesday.
Reactions
Other world leaders have since commented on Truss's nomination.
French President Emmanuel Macron said on Monday he was "ready to work together as friends and allies" with Truss.
Elsewhere, Ukraine's president Volodymyr Zelensky said he believed "that together we will be able to do more to protect our peoples and to thwart all Russian destructive efforts," during in his daily address on Monday.
Under Boris Johnson, Britain was one of Ukraine's staunchest supporters following the start of Moscow's offensive in the former Soviet republic.
Meanwhile, Russia is not expecting any changes to its frosty relations with Britain.
"Judging by statements made by Madame Truss when she was still foreign minister... one can say with much certainty that no changes for the better are expected," Kremlin spokesman Dmitry Peskov was quoted as saying by the state TASS agency.
