Get ready for backbench Boris.
After more than three years as prime minister, Mr Johnson heads for the backbenches, where he is expected to be defiant, stir up trouble and plot a Trump-style comeback.
Although he vowed in his farewell speech outside a packed Downing Street on Tuesday morning to "get behind Liz Truss every step of the way" and hinted that a comeback is not on the cards, nothing is for certain.
"Mission largely accomplished - for now!" he declared at his final prime minister's questions in July.
Top Tories, close allies and even an ex-girlfriend are all agreed that his resentment towards his assassins - as he sees them - means he will bide his time until he is ready to strike back.
And as he heads for the backbenches, the former prime minister is walking into an almighty row already, as the old wounds that led to his downfall are reopened.
The inquiry by the Commons privileges committee into claims he lied to MPs over partygate and about groping allegations against former deputy chief whip Chris Pincher could lead to him being suspended or even being kicked out of the Commons.
A legal opinion by top QC Lord Pannick that the inquiry is "fundamentally flawed" - commissioned by Mr Johnson's government - has prompted demands from his allies, who have condemned the probe as a "witch-hunt" and a "kangaroo court", for the inquiry to be scrapped.
Ms Truss signalled during the Tory leadership campaign that she would vote to call it off, a move that would engulf her in a damaging cover-up and cronyism row. But there will be a furious battle over the inquiry as MPs return to Westminster after the summer recess.
On the backbenches, Mr Johnson will no doubt seek to defend his legacy and is tipped to speak out on causes he cares about, such as net zero, levelling up and Ukraine, where there are four streets - and a cake - named after him.
He's also joining on the backbenches another former Tory prime minister, Theresa May, whose demise he plotted with his Brexiteer allies after he resigned as foreign secretary in 2018.
Who will Speaker Sir Lindsay Hoyle call first in debates and ministerial statements? Parliament's rulebook Erskine May (no relation!) offers no guidance.
Mrs May, first elected in 1997, has been an MP longer, though Sir Lindsay might use his discretion to call Mr Johnson first on some issues, like Ukraine, for example.
Johnson has form for causing trouble on the backbenches
It is unusual but by no means unprecedented for there to be two former prime ministers on the green benches behind the current incumbent of 10 Downing Street. And the precedent of backbench back-seat drivers doesn't bode well.
While Harold Wilson and James Callaghan both sat on the Labour backbenches from 1979 until 1983, Sir Edward Heath's portly frame filled the corner seat below the gangway, just feet from the prime minister and the despatch box, for 27 years from his February 1974 general election defeat until he left parliament in 2001.
He was joined on the backbenches between 1990 and 1992 by his sworn enemy Margaret Thatcher after she was ousted in a Cabinet coup, and by John Major after his defeat in Labour's 1997 landslide.
Sir Edward's sour backbench vigil and 25-year feud with Mrs Thatcher earned him the nickname "the incredible sulk". And Mrs Thatcher clashed with Mr Major over his handling of the economy just weeks after he succeeded her in 1990.
Mr Johnson, of course, has form for causing trouble from the Tory backbenches. Within days of resigning as foreign secretary over Brexit in July 2018 he exploded back into the political fray with a blistering broadside as Mrs May struggled to contain open warfare in the Conservative Party.
He complained that a "fog of self-doubt" had descended on the government and accused the PM of misleading voters and putting the UK "in limbo". And making a clear pitch for her job, he added: "It's not too late to save Brexit."
PM has consistently refused to rule out a comeback
A few weeks later, at the 2018 Tory conference in Birmingham, he again launched an explosive attack on Mrs May's Chequers plan for Brexit. "Chuck Chequers!" he bellowed to 1,500 adoring activists at a fringe meeting.
This time it's different, however, he claims. "My intention and what I certainly will do is give my full and unqualified support to whoever takes over from me," he said during his farewell tour last week.
And in this weekend's Sunday Express, he wrote: "This is the moment for every Conservative to come together and back [the] new leader wholeheartedly."
And yet Mr Johnson has consistently refused to rule out a comeback, no doubt flattered by a Sky News-YouGov Tory leadership poll which suggested nearly half of Conservative Party members want him back.
When asked "What if Boris Johnson was actually on the ballot paper?" he won by a landslide. Some 46% said they would vote for him - almost double the 24% for Liz Truss and 23% for Rishi Sunak.
Talk of 'seven-figure sum' for Johnson's memoirs
There was also a "Bring Back Boris" petition, organised by Tory donor Lord Cruddas, demanding a rule change so the outgoing PM could join Liz Truss and Rishi Sunak on the leadership ballot paper.
Former Tory cabinet minister Rory Stewart has compared Mr Johnson to former Pakistan PM Imran Khan, Italy's Silvio Berlusconi and his soulmate Donald Trump in hoping for a return.
The Sunday Times quoted a senior government official claiming: "Boris is now getting two lots of advice. Some people are telling him to go away and have a nice life and make lots of money. Others are fuelling the stab-in-the-back theory and are suggesting to him that he could come back."
And what about money? It has been claimed that Mr Johnson hopes to make as much as £10m in his first year out of Downing Street.
Tory ally Lord Marland claims Mr Johnson's priority is "putting hay in the loft" to pay off his debts. He will be able to claim up to £115,000 of taxpayers' cash a year towards "public duties".
There is already talk of a deal worth a "seven-figure sum" for his memoirs, in excess of the £800,000 for David Cameron's, as well as finishing a book on Shakespeare.
Then there's newspaper columns - he did, after all, call The Daily Telegraph his "real boss", according to Dominic Cummings - and signing up with a speakers' bureau for £250,000 a speech.
Of course, he'd have to declare his earnings if he remains an MP, although he has fallen foul of the rules of the Register of Members' Interests before and clashed with parliament's standards commissioner and the Electoral Commission over late declarations, a holiday in Mustique and "wallpaper-gate".
'I would never write him off'
He will need to remain in the Commons, though, if he does plan a political comeback. If he survives the privileges committee inquiry or it's thrown out in a Commons vote, at the next election he will defend a majority in Uxbridge and South Ruislip of 7,210, not the most impregnable given the Tories' falling support in the polls.
A clue to Mr Johnson's intentions - whether he will indeed be loyal to his successor or cause trouble - will be whether he plans to attend the Tory conference next month.
As he demonstrated with his 2018 onslaught on Theresa May, he enjoys a status with party activists of somewhere between a god and a rock star. His reception from those adoring activists would overshadow and humiliate his successor.
In a farewell interview with the Daily Express, Mr Johnson said it was "TBC" whether he would attend the Conservative conference this year. So he's not ruling that out, either.
Questioned about his old boss's intentions on Sophy Ridge on Sunday on Sky News, Mr Johnson's veteran ally Lord Lister predicted: "I'd never say on anything with Boris Johnson. Anything is possible in the future."
And repeating a famous Boris Johnson quote from 2013 on his leadership ambitions, he added: "If the ball comes loose in the scrum, then anything could happen. I would never write him off."
'Hasta la vista, baby'
The last word on backbench Boris's intentions for the future goes to his former girlfriend Petronella Wyatt, who had a four-year affair with him when they worked at The Spectator magazine, which he edited.
"Knowing Boris as I do, there is no doubt he is planning a political comeback," she tweeted last week. "If he wasn't, he would disassociate himself from the members' petition asking for a vote on his resignation.
"He has not once denied rumours that he intends to return."
At his final PMQs, as well as saying his mission was "largely accomplished - for now", Mr Johnson repeated Arnold Schwarzenegger famous catchphrase "Hasta la vista, baby", which roughly translated means: "See you later."
He also offered this advice to his successor: "Always remember to check the rear-view mirror."
Sound advice as the former PM becomes backbench Boris.