Rory Stewart has revealed he did not meditate for five or six days following his loss in the Conservative Party leadership race in 2019.
Mr Stewart was left disappointed by the result to an extent where he was "boiling with rage".
Boris Johnson took a resounding victory in the vote, with 66.4% backing the current Prime Minister in the 2019 vote, edging out Jeremy Hunt as the pair battled it out as the final two.
Mr Stewart was eliminated after the third ballot, as he failed to pick up enough votes to progress to the next round.
Rory Stewart admits that he felt a 'deep sense of betrayal' after Boris Johnson won the Conservative leadership contest in 2019. Stefan Rousseau
He has now opened up on the experience, admitting that he went on a silent retreat after finding out Boris Johnson would be the next leader of the Conservative Party.
Mr Stewart told Men's Health: "I had a sense of such deep disappointment that people I liked in the Conservative Party had endorsed and backed him.
"On that second retreat it took me five or six days to concentrate on meditation because I was boiling with rage. I couldn’t quite believe that anyone could think that he could be Prime Minister.
Boris Johnson won the Conservative leadership contest comfortably in 2019. John Sibley
"I felt a deep sense of betrayal. People I thought were honourable turned out not to be."
The former Conservative MP continued by taking aim at Boris Johnson, describing him as a "truly monstrous figure" but admitting that he feels "weirdly sorry" for him.
He said: "I feel weirdly sorry for him and guilty about how much I feel I have to attack him.
"He’s a truly monstrous figure, a figure from a morality tale: his appetites, his lies – it’s all so unreal. But I also feel the tragedy of it, what an awful life he’s leading."
Boris Johnson is facing fresh scrutiny over his knowledge of Chris Pincher's sexual misconduct allegations before they came to the fore publicly.
Downing Street said the PM failed to remember he had been told that Chris Pincher was the subject of an official complaint about his conduct.
The Prime Minister’s spokesman confirmed that Mr Johnson was briefed on the complaint by officials at the Foreign Office in 2019, a “number of months” after it took place.
The spokesman said the complaint against Mr Pincher – who was Europe minister at the time – was upheld although it did not lead to formal disciplinary action.
No 10 had previously claimed Mr Johnson had not been aware of any “specific allegations”, after Mr Pincher’s dramatic resignation last week as deputy chief whip following claims he groped two men at a private members’ club.