Britain First mayoral candidate Paul Golding turned his back on Sadiq Khan as the new London mayor gave his victory speech on Saturday morning.
Earlier on in the elections results, the announcement of Mr Golding's 31,372 votes was greeted by cheers from within the crowd.
But as Mr Khan stepped up to the microphone to give his speech, Mr Golding turned his back away from the audience and remained facing the wall until the mayor finished.
Congratulations for new London Mayor Sadiq Khan have come in from Labour MPs.
Streatham MP Chuka Umunna and former Labour leader contender Yvette Cooper took to Twitter to congratulate Mr Khan, who beat rival Zac Goldsmith on Saturday morning to the mandate.
Sadiq Khan won 1,310,143 votes in the London mayoral election, giving him the largest personal mandate of any politician in UK history.
The number of votes Mr Khan won compares to the 1,168,738 votes Boris Johnson won in 2008, and the 1,054,811 votes he received in 2012.
Thursday's election had the largest turnout in the history of directly-elected mayors in London.
Voters in England directly elect mayors, as opposed to prime ministers who do not receive a personal mandate from the electorate, instead winning office when their party secures enough constituencies.
Outgoing Conservative mayor Boris Johnson has congratulated Labour's Sadiq Khan on being elected his successor, and thanked Conservative candidate Zac Goldsmith for his "heroic efforts" during the campaign.
Zac Goldsmith has congratulated Sadiq Khan, who won the London mayoral contest, and thanked "the hundreds of thousands of people who trusted me today with their votes".
"I'm disappointed, of course, by the result - that I won't be able to deliver a manifesto that I'm proud of," he said, in a brief speech following the announcement of the mayoral election results.
Mr Goldsmith, the Conservative candidate, polled 994,614 votes, after second preference votes were taken into account, putting him second in the polls behind Mr Khan.
London has chosen "hope and unity" over "fear and division", Sadiq Khan said in his first speech as London Mayor.
The Tooting MP, speaking directly after his victory announcement, admitted the mayoral battle had not been "without controversy", in an apparent reference to alleged smear campaigns.
But he expressed relief that London had chosen hope.
"I hope that we will never be offered such a stark choice again", he said.
"Fear does not make us safer, it only makes us weaker and the politics of fear is simply not welcome in our city".
Khan made a promise that he would be a Mayor "for all Londoners".
Chancellor George Osborne has congratulated Sadiq Khan on becoming Mayor of London, adding that "we'll try to work together in the interests of London".
Labour's Sadiq Khan has won the London mayoral election, beating Conservative rival Zac Goldsmith.
Mr Khan took 1,310,143 votes after second preference votes were taken into account, while Mr Goldsmith took 994,614.
The Tooting MP had been the frontrunner in the counting process from early on, but final confirmation of his victory was delayed for several hours due to "discrepancies" in the ballot counting.
Speaking after the announcement of his win, Mr Khan said he was "humbled" by the result, and promised "to always be a mayor for all Londoners".
He said: "I'm so proud that Londoners have today chosen hope over fear and unity over division."