Weather presenter Alex Beresford has said "it can literally happen to anybody" after his cousin was stabbed to death in west London.
Nathaniel Armstrong, 29, was killed in Fulham just days after Beresford made an impassioned on-air speech about knife crime on 5 March.
The Good Morning Britain weather presenter told the ITV show on Wednesday: "No one would have expected it, especially after I spoke out.
"You couldn't make it up.
"It's come as a big surprise that it's happened to Nathaniel… he is 29, not in a gang, he went to a good school, university…"
He added: "He was a big guy. He was like 6ft 6in, 6ft 7in – when you spoke to him you were literally looking up.
"I guess on the outside some people could have been intimidated by him but he wasn't that person – everyone said he was a big friendly giant.
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"For this to happen to him, everyone was quite shocked. He wasn't really a fighter, he was someone who would talk his way out of something."
Mr Armstong was stabbed 11 days after the weather presenter said prison was "not a deterrent" as he intervened in a knife crime debate on Good Morning Britain.
He was knifed around 100 metres from his home in Gowan Avenue, Fulham, in the early hours of Saturday 16 March amid reports of a fight.
No arrests have been reported since Mr Armstrong's death.
Beresford said of the recent spate of stabbings on Wednesday: "I understand why people will look at it and say this is a black problem… it's not, it's a problem up and the down the UK in lots of different communities."
He added: "It literally can happen to anybody. That's why I was saying on the show, it is about environment.
"Poverty, we have not solved that, this is why a lot of people are finding themselves in these situations… something just needs to be done.
"I think this happening only reaffirms what I was saying about the environment and also about prisons and that they are not always a deterrent."
Beresford continued: "There are some people that will be deterred by a bigger (prison) sentence but for lots of boys that are committing these crimes, they don't care.
"If you are prepared to pick up a knife and stab someone, or risk your own life, you are prepared to give your life, it's not a deterrent.
"This person who has done this to my cousin, he has also ruined his life, the ripple effect goes wider, it affects his family as well."
Asked about what happened to Mr Armstrong, he said: "The person, we can't find him at the moment. Nathaniel is not here to tell his side of the story.
"We have seen the CCTV where they are talking… they disappear off camera and what happened, happened.
"As I understand it, it was a single stab wound that took his life."
Mr Armstrong was killed on the same street where TV presenter Jill Dando was murdered 20 years ago.