Boris Johnson found a video to send to Rishi Sunak calling him a “c**t”, his former spin doctor has revealed.
The former PM was furious when Mr Sunak decided to quit as chancellor.
Guto Harri, who worked as Mr Johnson’s director of communications, said he saw it as “the great betrayal of all time”.
In a new podcast on his time in No10, he said: “Rishi walked out. Didn't even tell Boris he was going to go.
“Basically, he went public with a resignation.”
Mr Harri added: “A few days later, Boris found a little video on the internet that expressed what he wanted to say to Rishi.
“He didn't send it, but he sent it to me and said, ‘thinking of sending this to Rishi.”
The video concluded with the message: “You’re a c***.”
Mr Harri went on: “So, there you have it. If you really want to know how Boris Johnson felt about Rishi Sunak in the immediate aftermath of his toppling and the great betrayal of all time as he sees it, there you have it.”
Ahead of Mr Sunak's resignation, Mr Johnson apparently became frustrated with the chancellor acting "like a bank manager.
"There was a moment where Boris blew up," said Mr Harri. "Sadly, Rishi was not in the room. He needed to know but Boris just basically went, f*** this s***, man, f*** this s***.
"We need to clear out the Treasury. The Treasury is acting like a bank manager, not an engine of growth. We need Singapore-on-Thames. We need dynamism.
"We're not here to just manage the decline, we need the growth engine of the British economy to be humming. And so, this tension was building and that was far more significant in the end, behind the scenes, than any row over Partygate or the trivial nonsense of everyday politics.
"This was a fundamental disagreement of policy that explains the fault lines that are still at the heart of the Conservative Party.’
Mr Harri, who was drafted into No10 in Mr Johnson's final months as PM, said the ex-PM believed Tory MPs were "psychotic" as they exerted pressure on him following a series of scandals.
"Something was happening to Boris, that he'd never had to deal with before," he said. "He was in real trouble. Big trouble. Conservative MPs in his words had become psychotic.
"The police were trawling all over Partygate and an inquiry led by an – until then, at least – obscure civil servant called Sue Gray, now a household name of course and a hero of the left, was planning what he described then as an orgy of pain, abuse and humiliation."
The latest revelations come after the communications adviser claimed earlier this week that Mr Johnson repeatedly denounced Ms Gray as a “psycho” as he raged about the Partygate investigation.
He said the disgraced ex-PM nicknamed her “Psycho Sue” as he became frustrated that his lockdown-busting boozing in No10 was being probed.
Ms Gray, who was a senior civil servant, was drafted in by Mr Johnson to examine the party allegations, before the Metropolitan Police launched its own inquiry.
The first episode of Unprecedented is available on Global Player.
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