It was a day that started with promise for the former London mayor and Conservative leadership frontrunner.

Eastern Daily Press: Boris Johnson speaks during a press conference at St Ermin's Hotel in London, where he formally announced that he will not enter the race to succeed David Cameron in Downing Street. PRESS ASSOCIATION Photo. Picture date: Thursday June 30, 2016. See PA story POLITICS Conservatives Johnson. Photo credit should read: Stefan Rousseau/PA WireBoris Johnson speaks during a press conference at St Ermin's Hotel in London, where he formally announced that he will not enter the race to succeed David Cameron in Downing Street. PRESS ASSOCIATION Photo. Picture date: Thursday June 30, 2016. See PA story POLITICS Conservatives Johnson. Photo credit should read: Stefan Rousseau/PA Wire

With the public backing of a number of MPs - and more set to come - Boris' overflowing ambition looked set to crystallise into a leadership bid.

Until a huge grenade by the man he had stood side by side with to tell Britain to vote for Brexit was lobbed into the contest.

Conservative leadership battles are always messy, but the full horror of the treachery, and the raw emotion was played out in hotel room not far from Downing Street, the home the hopefuls are eyeing.

Michael Gove's timing could not have been better for full humiliation.

As Theresa May set out a measured and sensible bid, even telling those listening she doesn't drink in the bars, Mr Gove announced that despite multiple denials, including an offer to sign a parchment in blood that he did not want to be prime minister, he would after all be standing because Boris was not the man.

It seemed every journalist based in Westminster was there waiting in anticipation.

Boris usually wants the full media limelight. Today he arrived through a backdoor avoiding the multiple TV crews he had invited along the night before.

It seemed the plan was to continue. He started with a speech which felt like a leadership bid with his vision for the success of London to be replicated around the globe.

The payoff was that he was not going to stand and with that he left - no questions, no jokes.

Loyalist and old friend James Cleverly, visibly distressed, spoke to the waiting media.

Most of the supporters - so jubilant just moments before - left quickly.

Some of his supporters had not even turned up.

St Ermin's hotel in St James's Park is a place where many political plots have been hatched.

On Thursday it was the stage where a long-planned path to power came to an abrupt dead-end. Michael Gove was nowhere to be seen.