Hampstead's vacant seat has returned to a Liberal Democrat candidate for the second time in a fiercely fought by-election.
Cllr Linda Chung won Hampstead Town's by-election with 919 votes.
Conservative Alex Andrews came in second with 620 on the day that Boris Johnson announced he was stepping down.
Labour's Alexandra Sufit was third with 559 votes.
Green Party's Patrick McGinnis received 104 votes, followed by independent candidate Jonathan Livingstone (44) and Peter McGinty (1).
The by-election was called when Labour paper candidate Adrian Cohen resigned less than three weeks into his time as a councillor, after his shock win on May 6.
"I'm astounded," said Linda. "I'm shocked but happy. I'm looking forward to being back in the council chamber. I love the cut and thrust..
She said she believed her win was because she's "continued working in Hampstead" since being a Camden councillor from 2008 to 2014.
"They all know I've got a good record of working. I don't think I was lax on any issues relating to Camden".
A trustee of multiple committees and organisations including Hampstead Community Centre and Burgh House, Cllr Chung has been involved with planning, environmental issues, policing, health and in democracy "and I always believe we can do better" she said.
"Things I'm keen on I've never stopped doing."
She said second time around she would take things in her stride, highlighting a need for "joined up thinking" on issues such as parking and littering.
"I don't want to get frustrated this time. I've been through it all before and this is why I wanted to do it again. I've learnt a lot and I've got broad experience."
She said she will continue her involvement with the neighbourhood policing, the Met, the GLA and the Mayors Office for Policing and Crime( MOPAC).
"They are really dysfunctional in my view," she said, adding that the treatment of Child Q, a school girl strip searched by police officers in Hackney, "was appalling".
"I shall continue with that work," she said. "I think it's very important for basic dignity and safety."
Tom Simon, Lib Dems leader of the opposition, said he was " very pleased" about the win.
"One thing that's really clear about it is we ran a very respected local candidate who is well known in the community for all she's done.
"It shows that the result in May was not really a pro Labour vote, it was more anti-Conservative.
"A lot of people in Hampstead are not happy with the government and not really happy with how the council is running things.
"The way their candidate stands down shows how Labour doesn't take Hampstead seriously. They've slipped back into third place."
Cllr Chung's win has increased the Lib Dem presence in the council to five after fellow Lib Dems Judy Dixey and Jonathan Kirk won Belsize Park in May, and Nancy Jirira was re-elected in Fortune Green.
"It cements our position in the council. We're a viable opposition to Labour.
"It's the first time we've taken a seat off them since 2007."
Alex Andrews, said she was "obviously a bit disappointed".
She said people on the doorstep were "really talkative", adding: "The two issues I heard was Adrian Cohen standing down at huge cost and that they specifically wanted to make a protest against Boris."
Due to a neck injury she was unable to go out to try to win last-minute votes.
"I'm really proud of the team. We ran a fantastic campaign.
"In another climate the result might have been different."
Labour candidate Alex Sufit, who came second in May, said, before the result was drawn: "We certainly put our oar in, we campaigned very hard.
"I'm pleased we were three women standing for the main parties. We need more women in politics."
Cllr Lloyd Hatton, Labour's group whip, said after the count: "It was an uphill battle, it's the biggest campaign we've run (in Hampstead) for many years.
"In Camden as a whole there's a good turn out for Labour."
The turnout was 37.6%
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