Brexit campaign boss Michael Gove's fury at seeing his colleague relaxing with Princess Diana's brother Earl Spencer sparked one of British politics' biggest betrayals, The Sun reported, citing Andrew Gimson's new book 'Boris: The Adventures of Boris Johnson'.
Foreign Secretary Johnson also blundered by holding a boozy barbecue at his 1.5 million pounds farmhouse the next day, and by failing to gain Tory leadership rival Andrea Leadsom's support, according to the book.
But he would leave Johnson's life-long ambition to be Tory leader in tatters after an extraordinary 11th-hour knifing as he made his own pitch for the top job, the report said.
In the book, acclaimed author and Tory insider Gimson Gimson pours scorn on Gove's "vanity-driven attempt to stab his friend in the back" and confirms that it was propelled by his columnist wife Sarah Vine, 49.
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Gimson describes one of the most turbulent leadership contests of all time in the wake of former Prime Minister David Cameron's resignation in June.
Gimson's book, with accounts from key insiders, shines new light on the rampaging egos, catastrophic errors and most treacherous week in Tory Party history.
It says the relationship between the Leave figureheads crumbled hours after they publicly embraced and celebrated the 52 per cent Brexit vote on June 23.
And Gimson says Gove was enraged by Johnson's lack of focus in the days after Remain campaigner Cameron quit.
The day after the Brexit victory, Johnson went to the Althorp estate in Northants to compete in Earl Spencer's annual cricket match against the Johnson family.
The following day, Johnson, 52, held his barbecue in Thame, Oxfordshire.
"Team Gove were invited to this festivity, and were appalled by what they saw as the lack of professionalism in the Boris camp," Gimson says of the Sunday bash.
Gimson also writes about Johnson's failure to gain leadership dark horse Leadsom's support. He is said to have forgotten to give her a letter promising her a Cabinet role.