Baldwin Luigi Singh, a nursing student, said he wanted to protect his younger brother from the bully who had threatened to beat up his brother.
But the suspect, detained by police along with another of his mate being suspect, has accused Singh of hitting his younger brother. Singh denied the allegation.
Singh's 13-year-old brother has not been named for being a minor. Police have confirmed the incident.
Both Singh's and the suspect's younger brothers have a history of bad blood, going back two years when they first got into a fight over a football game, according to The Straits Times.
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Things went downhill last Friday when Singh decided to go with a classmate to meet the suspects at a playground.
Singh claims the suspect walked towards him with a knife hidden in a plastic bag and stabbed him in the chest.
Singh, his brother and friend ran away from the scene. He went to a family clinic and sought medical help while waiting for an ambulance.