Boris Johnson blamed successor Sadiq Khan for the collapse of the Garden Bridge project while being quizzed over his handling of the doomed scheme.
The former mayor of London said he would have continued with the abandoned project were he still in City Hall.
He claimed "not a single penny of taxpayers' money" was wasted on the bridge while he was in charge.
A spokesman for Mr Khan said there was a "catalogue of failures" with the scheme on Mr Johnson's watch.
The current mayor abandoned the bridge plan after a report found it could cost over £200m.
During a hearing held by members of the Greater London Assembly oversight committee, Mr Johnson was repeatedly pressed by Labour AM Tom Copley on why he had "watered down" the conditions attached to a mayoral guarantee he gave the scheme in April 2016.
Mr Johnson said: "As for my motives at the time, all I can say is they may very well have been the same as the motives of the current mayor when he said that the Garden Bridge was a project to rival New York's High Line and he should certainly proceed with it.
"That, at this distance in time, is the closest I can get to analysing my motives."
He also admitted people involved with the project at Transport for London (TfL) would say it had been "rough around the edges".
But he dismissed suggestions the TfL board was kept at "arms length".
Analysis by BBC London political reporter, Susana Mendonça
As the freezing snow swirled around outside City Hall, a blast from the past blew in and Boris Johnson slid straight into what one assembly member described as his "usual tricks".
He regularly changed the subject from how public money was spent on the Garden Bridge during his time as mayor of London to other completely unrelated issues like Tube fares and Crossrail.
Did the London Assembly get what it was after? In a nutshell, no.
The Foreign Secretary denied the procurement process for the Garden Bridge project had been mishandled, accepting only that "bits and pieces were rough around the edges".
Asked if he had any regrets, his only one was that he didn't start the project sooner to get it completed before he had left the role of mayor.
And he turned the blame on to others, in particular his successor Sadiq Khan who Mr Johnson claimed had never given the project the "political push it needed."
In total, an estimated £46.4m of taxpayers' money - calculated as direct grants of about £26m from the Department of Transport (DfT), around £11m in services in kind from Transport for London (TfL) and the remainder in cancellation costs - was spent on the project which would see a bridge covered with trees built over the River Thames.
Mr Johnson said the bridge would have satisfied transport needs, and described its cancellation as a "bitter disappointment".
A spokesman for the Mayor Khan said: "The mayor welcomes Boris Johnson answering questions on the Garden Bridge, given the catalogue of failures that occurred around the project under his watch, and the tens of millions of pounds of taxpayers' money wasted.
"When Sadiq took over as mayor, huge outstanding issues remained around the Garden Bridge, with the project facing spiralling construction costs, a funding gap of over £70m and no agreement on how to fund maintenance costs."
Garden Bridge timeline
- The idea of a "floating paradise" as a memorial to Princess Diana was suggested by Joanna Lumley as far back as 1998
- The plan gathered momentum in 2012 and the following year then mayor Boris Johnson supported the scheme, pledging Transport for London would help deliver it. It was also backed by then Chancellor George Osborne
- Planning permission was granted in 2014
- The scheme was beset by problems over its funding and lacked support of some local residents
- In September 2016, Mr Khan ordered a review to find out if value for money was being achieved
- In October 2016, the National Audit Office revealed David Cameron ignored the advice of his own civil servants not to provide further taxpayer funds to the Garden Bridge Trust because of the risks of it not going ahead
- In January 2017 accounts filed with Companies House showed a £56m shortfall in the trust's accounts
- In April, Dame Margaret Hodge concluded it would be better to ditch the project rather than risk uncertain costs
- Following this report, Sadiq Khan withdrew his support