Television Alex Beresford paid tribute to the murdered cousin, saying that the death of a "bright young man" is "another example of unnecessary life lost from foot crime."
Nathaniel Armstrong, 29, was killed in western London on Saturday, 11 days after Beresford, who appeared in ITV's Good Morning Britain, made a passionate speech in the air for street violence.
Armstrong was pierced early in the morning about 100 meters from his home in Fulham, amid reports of a brawl.
He died just 1 hour ago at Guang Guang Avenue, on the same street where TV presenter Jill Dundo was killed 20 years ago.
In a statement, Beresford said: "I'm deeply sad that I confirmed that my cousin Nathaniel lost his life on Friday night. We were all so shocked to receive these news yesterday and our thoughts are now with his mother, his brother and sisters.
"Nathaniel was a bright young man with all his life in front of him, and this tragedy is another example of an unnecessary life lost from foot crime."
Friends remember Armstrong as "a great friendly giant" who loved basketball.
Beresford inserted a lively debate about the knife crime at Good Morning on March 5. Describing how he grew up in communities affected by crime with a knife, he said that prison was not an obstacle to the attackers.
"Some of these boys, they are not afraid of jail, if you do not change the environment will not change anything, and that's the key thing," he said. "This has been happening for years."
Detectives on Saturday said they were hunting a black man of 6 black cats during the killing, but no arrests.
One of Armstrong's friends who gave his name as George 30 said: "We do not know how this happened. There are many friends who live here." He was well-known in the local area.
"Everyone in the area would know him from basketball".
He added: "He was super-friendly, BFG. He looked awesome – six feet seven, big beard – but super-friendly. That will shock you how friendly he is."
DCI Glenn Lloyd, who heads the investigation, said: "We appeal for information from those who were outside and around in the area during the attack and I saw nothing of the note.
"My team is particularly interested in finding a black male on the high-light, about 6 meters high, who at the time of the incident was seen near the site."
Dando was 37 years old when he was shot in the head on the doorstep of her home at Guang Guang Avenue on April 26, 1999.