Boris Johnson has been sworn in at City Hall after his re-election as London mayor.
It was a surprisingly narrow victory that saw him beat rival Ken Livingstone.
The Conservative polled 1,054,811 to the Labour's candidate's 992,273 following a deeply personal and bitter campaign battle that saw the two men clash furiously in public and in private.
Earlier today, Mr Johnson thanked Londoners for giving him a "second mandate".
Prime Minister David Cameron said he was "delighted to congratulate" with Boris Johnson's re-election.
Mr Cameron said:
– Prime Minister David Cameron
"I think it was a very strong campaign by Boris. It was based on his record, on the excellent things he has done as mayor and I am delighted to congratulate him.
However, Ken Livingstone hit out at Boris Johnson on Saturday, describing him as a 'do-nothing Mayor'.
"With the exception of this rather silly little cable car there's nothing else he has started. If we have another four years like that then by the end of this decade London will be insufferable."
Mr Johnson failed to secure the massive win predicted by polls over recent days that had put him as far as 12 points ahead.
Early results in the contest also suggested the incumbent was significantly in the lead and even senior Labour figures conceded the Tory was poised to win.
But later count declarations saw the gap reduce, fuelling speculation Mr Johnson's victory was not the done deal that had been tipped.
No candidate won enough votes in the first round to secure victory, meaning second preferences had to be counted.
Liberal Democrat Brian Paddick was pushed into a humiliating fourth place after polling 91,774 votes, compared to the 98,913 secured by the Greens' Jenny Jones.
Political newcomer, Independent Siobhan Benita, took fifth with 83,914.
Ukip's Lawrence James Webb polled 43,274 while the British National Party's Carlos Cortiglia came last with 28,751.
Counting, which is carried out electronically, was dogged by delays, pushing back the result back significantly on original predictions that it would be announced in the early evening.
They included a power cut at Alexandra Palace as well as the reprocessing of two mislaid batches of ballot papers in the Brent and Harrow constituency.
In his victory speech, on Friday night, Mr Johnson admitted it had been a "long and gruelling" campaign.
He paid tribute to his defeated rival Ken Livingstone saying: "Of all the left-wing politicians I can think of your long period in office... you have been the most creative and the most original.
"And, if only you will promise not to stand again, I much look forward to having that non-taxpayer funded drink that we have so far not managed to fit into our diaries."
He pledged to make sure Londoners, especially young people in the city, were "ready to take the jobs" that are being created.
Mr Johnson said he wanted to thank those who voted for him, those who did not and those who thought about it.
"I want to thank all of you for giving me a new chance and a new mandate to take us forward."
During his speech, Ken Livingstone dramatically announced his retirement from electoral politics.
"This is my last election," he told fellow-candidates and supporters at City Hall:
"Forty-one years ago almost to the day, I won my first election on a manifesto promising to build good council housing and introduce a free bus pass for pensioners.
"Now I've lived long enough to get one myself. I didn't think I necessarily would at the time.
"And since then, I've won 11 more elections and lost three. But the one I most regret losing is this. This is the defeat I most regret, because these are the worst times for 80 years, and Londoners needed a mayor to get them through this very difficult period by cutting fares, by cutting energy prices and putting people back to work building good council homes.
"I am sincerely sorry to those Londoners who desperately wanted us to win that I failed to do that and they will continue to bear the pain of this recession without any help from here in City Hall."
Ken Livingstone then added that Mr Johnson's victory could be a headache in waiting for the Tory leader David Cameron with many tipping Boris Johnson to push for party leadership.
So as one candidate bows out is this just the start for the victorious 'Bojo'?
A survey conducted by ITV News asked whether Boris Johnson would make a good Conservative party leader. Mr Johnson came third in the survey after David Cameron and William Hague. However, he came ahead of Ken Clarke, George Osborne and Theresa May.
The six candidates were ranked as follows:
David Cameron - 22%
William Hague - 13%
Boris Johnson - 12%
Ken Clarke - 8%
Theresa May - 3%
George Osborne - 1%The Index is conducted by ComRes on behalf of ITV News.
Boris Johnson himself told the BBC that he is dedicating himself to London and people could "take it for granted" that he would not stand as an MP at the 2015 general election.