Liz Truss speaking to ITV News in 1994
Ms Truss travelled to Balmoral on Tuesday, 6 September, to be formally invited by Her Majesty to form a new government.
Pictures from the meeting show the two smiling and shaking hands.
In a statement, Buckingham Palace said: "Ms Truss accepted Her Majesty’s offer and kissed hands upon her appointment as Prime Minister and First Lord of the Treasury."
But Ms Truss's feelings towards the monarchy have not always been unambiguously positive.
An interview with ITV News, recorded in 1994, has emerged in which the then student, who attended Roundhay School in Leeds, said she was "against the idea that people can be born to rule".
Ms Truss, who was 18 at the time, said in the clip: "I'm not against any of [the Royals] personally, I'm against the idea that people can be born to rule – that people, because of the family they are born into, should be able to be the head of state of our country. I think that's disgraceful."
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At the time, Ms Truss – the daughter of parents she described as "left wing" – was a member of the Liberal Democrat Party. The interview was recorded at the party's conference in Brighton, during which Ms Truss spoke on stage in favour of a motion to abolish the monarchy.
In her speech she said: "Everybody in Britain should have the chance to be a somebody, but only one family can provide the Head of State.
"We Liberal Democrats believe in opportunity for all, we believe in fairness and common sense."
She later joined the Conservative Party and told reporters she realised that her anti-monarchist stance was a mistake "almost immediately".
"I was a teenager at the time and I do believe that people who never change their mind on anything and think the same at 16 as they do at 46 are, well, first of all, they're not normal people like I am," she said.
She also described herself as a "professional controversialist".
It has been pointed out that her politics have evolved in other areas as well, including on the issue of EU membership. She campaigned to remain in the union at the 2016 referendum, before
This week, her remarkable political journey culminated when the now 47-year-old was selected by fellow party members to lead the Conservatives – and by extension the country – following the resignation of Boris Johnson.