Following two recounts in the constituency, counting was suspended as staff were sent home to rest on the morning of June 9.
At this stage there were reports that Lady Borwick had lost to Labour candidate Emma Dent Coad and on Friday evening, after a third recount, it was officially announced that Labour had won the seat by 20 votes.
It was the final seat to be declared in the 2017 General Election and one of several shock outcomes.
The Conservatives lost their majority in parliament but are seeking to form a government with the backing of the Democratic Unionist Party.
Kensington has been a safe Tory seat but it also voted to remain in the EU in the Brexit referendum. In contrast, Borwick supported leaving the EU and Labour actively targeted ‘remain’ voters during the election campaign.
Borwick, a former director of the Olympia Fine Art and Antiques Fair for several years and deputy to Boris Johnson as Mayor of London before she became an MP, won the seat in 2015 with a majority of 7361.
In her speech after the result, Borwick said: "I wish Emma every success, but please be assured, as far as I am concerned, tomorrow I start the fight back for Kensington and the Conservatives."
Antiques industry advocate
She has been a vocal champion of the art and antiques sector in parliament, most recently speaking out in defence of the continued trade in antique ivory.
At ATG's seminar on CITES in January, Borwick appealed for unity between dealers and auctioneers in presenting the industry’s case for antique ivory to the government.
British Art Market Federation chairman Anthony Browne said: "I am very sorry that Victoria Borwick has lost her seat by such a narrow margin. She has been a stalwart supporter of the whole art and antiques sector on a wide range of issues. There are so few parliamentarians with a knowledge of our market and she has demonstrated great dedication to championing the art market."
Marco Forgione, chief executive at the BADA, said: "The result in Kensington is shocking. Victoria has been a tireless campaigner on behalf of the trade in Westminster, fearless and dedicated in standing up for the fine art and antiques sector. Her common sense and practical advice will be sorely missed in Parliament."
The Kensington seat has been Conservative since its creation in 2010 and the party has held its predecessor, Kensington & Chelsea, in every General Election.