A young father collapsed and died reportedly after taking part in a dangerous game where people punch each other as hard as they can and film it.
Tommy Main, 23, was at a party in The Nursery, Erith, when he suffered a cardiac arrest on Saturday night.
Emergency services rushed to the scene and tried to save him but he died a short time later.
The game called 'Punch4Punch' sees two people taking turns to hit each other until one gives up, sometimes drinking alcohol as a forfeit and the footage is then posted online.
A 20-year-old man was arrested on suspicion of murder and has been bailed until late September.
Social media has been flooded with tributes to the former Erith School pupil from family, friends and people who didn't even know him.
Brother Benjamin wrote online: "Tommy, I love you so much boy.
"I'm a broken man without you here with us. I'm going to miss you so much baby bro."
Mr Main's mum's cousin Angela Martinelli said: "He was a wonderful single dad.
"Last week he mentioned going on YouTube to learn how to plait his little girl's hair. I do not know of many dads who would take the time to do that.
"I was told by a relative that there was some punching game going on and clearly Tommy had a severe punch that would cause what they consider, a heart attack."
Brother Roy slammed the "so called friends" at the party for filming the punching game.
He said: "I had to say goodbye to my little brother today for the last time.
"I'm hurting so bad, I'm so sad I love you Tommy Main."
A tribute page was set up by best friend Matthew Davey and attracted more than 1000 'likes' after just a few hours of going online.
Mr Davey said: "He was my best friend in the whole world."
Mr Main's Facebook page is flooded with pictures of his young daughter Aimee, four, whom friends say he doted on.
Ronnie Marie said: "RIP my babe always in my heart never failed to make people smile can remember us as kids can't believe ur gone fly high sweet dreams xxxxxxxxxx."
A friend, who didn't want to be named, told News Shopper Mr Main was taking part in a 'punching game' which went wrong.
A spokesman for the London Ambulance Service said: "We were called at 12.24am on Sunday to The Nursery in Erith to treat a young man in his 20s for a cardiac arrest.
"We sent two single responder cars and an ambulance crew to the scene.
"The patient was taken to Darent Valley Hospital as a priority, despite our efforts the patient sadly passed away. A doctor confirmed the death at 1.28am."
A Met Police spokesman added: "The death is being treated as unexplained at this time. Enquiries continue."
- UPDATE: Girl taken to hospital after being hit by car in Darenth
- UPDATE: Eight mile queues on M25 after police rescue man from Dartford bridge
- Cray Wanderers stadium plans vetoed by Sadiq Khan - but refusal could be reversed as decision is called in
- PARTY TIME! Send us your school prom photos for our gallery
- 'I was told I don't look British': Lewisham parents take a stand against racism as hate crime soars after EU referendum