Danny Humble, 35, was brutally attacked close to Romsey Close in the town as he walked home from the pub in May last year.
What started as an initial light-hearted exchange between him and a group of teenagers, who had said he looked like Ant McPartlin, rapidly degenerated into violence and Mr Humble was punched, kicked and stamped on.
A blow to his head or neck ruptured a blood vessel. He was rushed to the RVI but doctors were unable to save him and he died a day later.
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The deadly assault lasted around just 15 seconds.
During a trial at Newcastle Crown Court, Ethan Scott, 18, of Chester Grove, Blyth, Alistair Dickson, 18, of Hawkins Way, Blyth, Bailey Wilson, 18, of Mitford Avenue, Blyth, Kyros Robinson, 18, of Woodside Avenue, Seaton Delaval, and one youth, who cannot be named, all denied murder.
But today jurors found Dickson guilty of murder and the other four guilty of manslaughter.
Mr Justice Bennathan said he will sentence the teens at a later date and remanded all five in custody. He warned they all faced "significant custodial terms".
Prosecutor Jacob Hallam QC told jurors Mr Humble and his partner Adele Stubbs had been on their first night out after the lockdown restrictions were lifted and had spent the evening "having dinner, dancing and singing and drinking".
It was as they headed home, after a "really good night out" and drinking a "canny skinful" that they encountered the youths by chance, shortly after midnight.
Mr Hallam said other people were around that night and one person who witnessed the encounter heard some of the conversation between Mr Humble and the teens.
He told the court: "They were speaking to Mr Humble and, in his words, were 'just having a little bit of crack on', saying to Daniel Humble that he looked like one of the TV duo Ant and Dec.
"He recalled Mr Humble laughing and saying words to the effect of 'good one lads' and one of the group saying 'can I have your autograph, you are my inspiration'.
"He remembers one of the group saying 'yeah, he does look like him'."
The court heard Miss Stubbs was unable to recall leaving the last pub, but remembered being in the underpass and a confrontation starting.
Mr Hallam said: "She remembered seeing an upper cut being delivered to Mr Humble from his left.
"She thought the attack had began near the end of the underpass but moved onto a grass verge. She remembered a group of people around him, separating him from her.
"When she got to Daniel Humble, her partner, he was unconscious and was bleeding on the ground."
During the trial, jurors watched a video recorded police interview with Miss Stubbs, who said they had had a "really nice night, chatting about the future, life, our plans" before the fatal trouble.
She said: "We had a really good night. Next thing I remember is a group of lads either side of the underpass."
Miss Stubbs, who is a nurse, told detectives she did not have a clear memory of what happened in the underpass but remembered shouting "get off him, get off him".
She said: "It just went from zero to 100 so fast.
"Next thing I remember is up on the grass. I got to him and he was out, blood trickling from his mouth.
"Instinct kicked in and I knew something was really wrong. I started CPR. I couldn't look at his face because I knew.
"I was shouting what the 'f' have you done to him.
"He wasn't breathing."
Miss Stubbs said she was taken to a police vehicle and added: "He was in the ambulance and the ambulance wasn't going. I was screaming 'why aren't they going' and she said they were still working on him."
Speaking after the tragedy, his mum Deb Humble said: “Danny was a devoted dad. He was a welder by trade and took great pride in his work but his first priority and most important job was always being a father.
“He was a family man and very close to his two brothers, the Humble brothers – the ‘Three Musketeers’ as they were known to us.
“He was also a great son, someone to be proud of, and a very loving boyfriend.
“Though he loved Cramlington, he was born in Newcastle and was a Geordie lad through and through; meaning another great love of his life was, of course, Newcastle United.
“We are lost without him – we are broken."
Two further teenagers were also initially charged with Mr Humble’s murder, but Izaak Little, 18, of Blackthorn Drive in Blyth and a 17-year-old, who cannot be named, were last month found not guilty at the direction of the judge.