Liz Truss was advised by the late Queen to 'pace' herself, the former prime minister has revealed.
Ms Truss met the monarch at Balmoral just two days before her death in September 2022.
In her upcoming memoir, the ex-PM admits she did not listen to the Queen's sage advice, in a 20-minute discussion between the pair.
Ms Truss's 49 days in charge were marked by economic turmoil – including reforms that sent the pound tumbling – before her ousting from Downing Street.
She writes of the late Queen in the book, Ten Years To Save The West, which will be serialised exclusively in the Mail from Saturday: 'She was completely attuned to everything that was happening, as well as being typically sharp and witty.
Liz Truss meets Queen Elizabeth II at Balmoral Castle two days before the monarch's death
'Ten Years to Save the West': Former Prime Minister Liz Truss's new book
'Towards the end of our discussion, she warned me that being prime minister is incredibly aging. She also gave me two words of advice: "Pace yourself." Maybe I should have listened.'
Summoned to Scotland due to the Queen's poor health, Ms Truss described her as 'frail' but 'alert', 'absolutely on top' of things and seemed intent on meeting again.
Liz Truss: A political memoir like no other
In her own words, the dramatic inside story of how she was driven out of Downing Street.
Starts exclusively in Saturday's Daily Mail.
Liz Truss delivers a speech on her last day as PM, outside No 10 on October 25, 2022
Upon news of the Queen's death – which came just days after Ms Truss entered No 10 – the former prime minister recalls thinking: 'Why me? Why now?'
The state ceremony and protocol that followed left her 'a long way from my natural comfort zone', she writes. Ms Truss said she broke down 'into floods of tears on the sofa'. She added: 'Once again the grief was mixed with a feeling of awe over the sheer weight of the event, and the fact that it was happening on my watch.'
Ms Truss admitted previous prime ministers may have been better suited to the events by providing 'the soaring rhetoric and performative statesmanship necessary'.
She said that, despite being under massive political pressure, her first meeting with King Charles sparked 'a bizarre sense of camaraderie between us, with both starting out in our new roles and having to navigate unfamiliar territory'. At the time, Tory MPs had already begun making moves to relieve Ms Truss of her duties. As she curtseyed to Charles, he said: 'So you've come back again?'
Ms Truss replied: 'It's a great pleasure,' but the King added: 'Dear, oh dear. Anyway…'
In an interview about her book last year with The Mail on Sunday, Ms Truss revealed her former friendship with Kwasi Kwarteng is effectively over.
Ms Truss fired Mr Kwarteng as chancellor in a last-ditch attempt to avert her demise.
Asked whether they are are still in contact, she said: 'Occasionally. I'm not speaking to him that much.'