Like Mr Gove - who infamously made a rival bid for the leadership after the referendum - Mr Johnson has always been suspected of aiming to lead the party and be prime minister.
Dominic Raab, a Brexit supporter and former housing minister, was appointed to replace Davis only days before negotiations in Brussels are due to resume next week. European Union officials have warned Britain repeatedly that time is running out to seal a deal spelling out the terms of the divorce and a post-split relationship.
Conservative lawmaker Michael Fallon, an ally of May, dismissed Johnson's "Brexit dream" rallying cry.
It was in the "ludicrous position" of offering to accept huge amounts of European Union laws that for decades British governments have argued against, yet with no say in how they are made.
Labour leader Jeremy Corbyn said the Prime Minister "has no authority left and is incapable of delivering Brexit".
Raab, who is promoted from housing minister, now faces the hard task of calming nervous Brexiteers within the Tory ranks who are threatening to derail Theresa May's plans.
The MP for Aylesbury campaigned to remain in the European Union.
Mr Davis's departure just 48 hours after being part of the Cabinet that agreed to Mrs May's plans also triggered the resignation of departmental ally Steve Baker, while fellow Brexit minister Suella Braverman is also reported to have stepped down.
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In a statement, May's spokesman said the prime minister will fight any attempt to oust her.
The following day, UK Foreign Secretary Boris Johnson - another key Brexit player, and someone who originally campaigned for Brexit back in 2016 - made a decision to follow suit. She complained that the backstop position on Northern Ireland "is not appropriate and should have..."
"If the Brexit deal is rejected by Parliament, then we, the people of Britain, should have the democratic right to determine our own future".
In 2016, following the resignation of Prime Minister David Cameron, Johnson was widely considered a front-runner in the race that May eventually won, but he ruled himself out after the defection of a key ally.
Inside, the paper's report says May finds herself in a "serious crisis" caused by her "inability" to manage an orderly Brexit.
"I don't think it's central to Foreign Secretary, but there you are".
May has hung on to power longer than many expected after she lost her majority in a June 2017 snap election that she had called in hopes of strengthening her hand in Brexit talks.
"That is why we are demanding a People's Vote on the final Brexit deal".