In February, he said that "given previous expenditure, the taxpayer will be better off if the bridge is built", but later announced plans to pull public funding.
'It is all the more disappointing because the Trust was set up at the request of TfL, the organisation headed up by the mayor, to deliver the project.
Khan wrote to Lord Mervyn Davies, Chairman of the Garden Bridge Trust, in April, stating that he was not prepared to guarantee the bridge's annual maintenance costs - which planning permission had relied on.
"The Labour Mayor claimed to support it but support it, but killed it out of spite because it was not initiated in his period of office".
A spokesman for the former mayor said: "So sad Sadiq Khan has killed the Garden Bridge and wasted so much time and money". A reported £37 million of public funds had already been spent on the project, money that will not be able to be recovered.More news: Trump lashes out at media after being forced to condemn Nazis
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"There was not an open, fair and competitive process around the two TfL procurements for the Garden Bridge Project".
The Garden Bridge has been controversial since its inception, even though it had Gurkha-rights campaigner Joanna Lumley behind it. Khan himself doesn't seem to have ever been that fond of the project, or at least the fact that it relied on public money, and put a halt to preliminary structural planning works previous year.
Originally estimated at 60 million pounds ($78 million), the project was likely to end up costing over 200 million, according to an independent review commissioned by Khan.
We are incredibly sad that we have not been able to make the dream of the Garden Bridge a reality and that the mayor does not feel able to continue with the support he initially gave us.
"I have been clear since before I became mayor that no more London taxpayers" money should be spent on this project and when I took office I gave the Garden Bridge Trust time to try and address the multiple serious issues with it.
Khan said he had taken the decision to withdraw support because of a continuing shortfall in fundraising for the scheme and the lack of the necessary land use agreements despite three years of talks. It blamed the London Mayor Sadiq Khan for failing to support it, but he hit back saying Londoners should be "very angry" that more than 30 million pounds had already been spent on the scheme.