Sadiq Khan has joked he’d beat Boris Johnson in a boxing match, declaing: “I could have him!”.
The mayor of London was invited to face off with his predecessor during a visit to a gym in Ilford, east London.
"He used to have a future," Mr Khan added, after Mr Johnson was forced from office and a comeback bid ended in failure.
The mayor was visiting the Box Up Crime scheme with Metropolitan Police Commissioner Mark Rowley - who was invited to sort out "security" for the bout.
The pair went to learn how it helps young people from the area by providing training, support and guidance.
The project was set up by Stephen Addison BEM in 2013 as a way of providing an alternative for youngsters vulnerable to crime.
It was launched with the help of Redbridge council leader Jas Athwal, and Mr Addison described the gym as a "home" to many of its users due to its tight-knit community.
Mr Khan described the project as "inspirational" and revealed how boxing had helped "transform" the lives of him and his brother when they were younger.
"When I was young, growing up in a council estate in south London, our local boxing club transformed the aspirations of my brother and myself," he said.
"The coaches there guided us towards constructive things to do, and boxing, like many other sports, can change people's lives and lifestyles."
Tory politicians have spent years pinning the blame on Mr Khan for knife crime in London.
But the Met Police’s new Commissioner Sir Mark Rowley, who joined Mr Khan on a visit, insisted London is “fantastically safe" as the force announced a drop in homicide rates last year.
The total number of homicides recorded under Home Office Counting Rules (HOCR) for 2022 is 109, which is 17% down on 2021, the Met said.
Nine homicides were gun enabled in 2022, which was a 25% fall and the lowest figure since 2014.
A total of 69 homicides were knife enabled, which was a 17% reduction and equal to the pre-pandemic figure for 2019.
