Police were called at 1.59pm on Wednesday to reports of a stabbing in Malyons Road.
Officers attended along with the London Ambulance Service and London’s Air Ambulance.
Mr Josephs was found inside his car, a grey coloured BMW, suffering from knife wounds.
Despite efforts to save him, he died at the scene.
His next of kin have been informed and continue to be supported by specially trained family liaison officers.
Four men, one aged 23, two aged 24, and one aged 25, were arrested in connection with the murder and have been bailed pending further enquiries.
Detective Chief Inspector Kate Kieran, who is leading the investigation, said: “This was a shocking incident that took place on a busy street in the middle of the day. There were a large number of witnesses and I thank those people who have already taken the time to share what they saw.
“If you have footage or information but haven’t yet spoken to police, please do get in touch.
“We are building a timeline of the events surrounding Alex’s murder and your information could be a missing detail in that picture. If you saw anything, please do take the time to contact us.
“Alex’s family is reeling from the shock of losing their loved one in such a violent way. Our thoughts are with them as our investigation progresses.”
Detective Chief Superintendent Trevor Lawry, leading local policing, said: “It saddens me to see another life ended by knife crime in our city.
“I know that this incident will send shock waves throughout our community. Please know that I share in your concerns, and while my officers are supporting the murder investigation team, they are also available to provide support and reassurance through enhanced patrols in the area.
“We believe that this is an isolated incident, however, if you are worried, please do feel free to approach officers and speak with them.”
Police are asking anyone with information or footage relating to te incident to call 101 or Tweet @MetCC quoting 3928/10May.
To speak with officers from the investigation team direct call 020 87214622.
To remain 100% anonymous contact the independent charity Crimestoppers on 0800 555 111 or visit Crimestoppers-uk.org.