A British weatherman whose cousin was stabbed to death in London earlier this year took center stage Wednesday when he told Mayor Sadiq Khan on national TV that he must be “more vocal on the issue of knife crime.”

The dramatic moment took place during ITV’s Good Morning Britain program, where the mayor clashed with hosts Piers Morgan and Susanna Reid about his policing priorities and the London Bridge terrorist. Topics ranged from why terror attacker Usman Khan was released early from prison to why London has been unable to adequately combat the stabbing scourge that's plagued the city for years.

At one point weatherman Alex Beresford joined the conversation and described the pain he's felt since the March murder of his 29-year-old cousin, Nathaniel Armstrong. He criticized Khan, who listened intently, for not being outspoken enough about the problem.

"I feel like you could be more vocal on the issue of knife crime,” Beresford said. "It's not just about saying all the right things, it's about doing the right things as well."

Mayor of London Sadiq Khan speaks during a vigil at Guildhall Yard in London on Monday to remember the London Bridge stabbing victims and honor members of the emergency services and bystanders who fought the attacker.

Mayor of London Sadiq Khan speaks during a vigil at Guildhall Yard in London on Monday to remember the London Bridge stabbing victims and honor members of the emergency services and bystanders who fought the attacker. (AP)

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He added: "We have got young kids walking around with knives, carrying them out of fear. That's not an excuse to carry a knife but it is a reason for it. And it is because our communities are completely infested with several different things — there are so many disadvantages going on that need to be addressed.”

When asked by another host about Nathaniel’s death, Beresford said “words can’t describe what it’s like to lose one of your cousins to knife crime."

“And unfortunately Nathaniel isn’t the only person that I know that has lost his life to knife crime,” he said. “It cuts you so deep inside, literally.”

Later in the segment, Khan told Beresford, "I'm as frustrated as you, man” and said the issue is “one thing that keeps me up at night,” according to The Sun.

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Armstrong was attacked in West London on March 16. The man accused of stabbing him during an argument was set to face trial in November, but had his murder charges tossed in June after prosecutors said there wasn’t a realistic chance of a conviction, according to the BBC.

As of Wednesday, the number of knife crime deaths in London this year is at 127, slightly below last year’s total of 139, The Sun reported.