Anthony Yarde has implored the country to obey the lockdown rules and ignore coronavirus conspiracy theories.
The world title challenger lost his dad and his gran to Covid-19 in the space of six days last month.
And with lockdown being eased in England this week, Yarde hopes his experience can convince others to think twice before flouting the guidelines.
"[Seeing people mingling] has made me feel angry, disappointed and upset because I've been through it," he told ITV.
"In the beginning I wasn't even leaving the house, even before the bad news, the deaths of my grandma and my dad led me to leave the house.
"When I see people in the parks mingling and talking, they know what's going on but haven't taken time to be considerate.
"It might not be them or someone in their family but a sneeze or a handshake and you could affect someone else.
"I just tell people to use their minds and think of their community.
"At my dad's funeral there were still people saying it's fake. It's not worth saying you're going to come and shake everyone's hands or hug everyone.
"There are all these conspiracy theories but no-one really knows so it's not worth the risk."
Yarde believes his dad and gran caught the virus on a trip to Israel and they passed away shortly after returning to the UK.
The 28-year-old, however, is determined to use his grief in a positive manner.
"You can't prepare for it; life is a journey, it's not really a destination pain is mandatory, whether it's emotional or physical," he added.
"People get emotionally stronger by going through pain. All forms of growth I believe have some sort of pain behind it; but it's early days to say if this will make me stronger.
"What I've learned is that some people don't want to me reminded, they just want a positive conversation, or a normal conversation.
"I messaged my closest friends and begged them to be normal, just banter me and cuss me about my big forehead."
