A youth accused of murdering a talented young footballer had been excluded from school at the time of the death, a court at the Old Bailey has heard.
Kiyan was a striker for QPR's youth team
The 16-year-old boy was play-fighting outside the London Academy in Edgware, north London, when Kiyan Prince, 15, tried to intervene, the court heard.
The accused then stabbed him in the heart, the prosecution alleged.
He denies murdering Kiyan on 18 May. The defendant earlier admitted Kiyan's manslaughter but the plea was rejected.
The teenager cannot be named because of his age.
Kiyan was described by a teacher as a "gorgeous boy... very popular and well-liked", said prosecutor Nicholas Hilliard, on the first day of the trial.
"The allegation is that this defendant murdered a 15-year-old boy by stabbing him in the heart with a knife," said Mr Hilliard.
"It is not in dispute that the defendant did that but his case is that it is not murder."
He said the accused had been banned from the London Academy at the time of Kiyan's death.
"There is no evidence of any bad feeling between the two of them," said Mr Hilliard.
Before the stabbing, the defendant had been involved in some play-fighting with another boy, said Mr Hilliard.
When Kiyan tried to intervene, the accused went up to him and said "What's going on?", the jury was told.
The accused allegedly pushed Kiyan who responded in kind. The youth then put his hand to his pocket, it is claimed.
Kiyan asked: "What is that?". As the scuffle escalated, the defendant allegedly grabbed Kiyan round the neck and stabbed him.
The court heard the defendant told officers he intended to leave "just a little scratch...but it went deep in... 'cos I never used a knife before."
When asked why he was carrying a knife, he claimed it was a "little toy" he carried around every day.
Teacher Liejhe Hernandez witnessed the play-fighting but called a colleague on her mobile when she saw the defendant push another boy against a car.
"I knew I had to get help," she told the jury.
She approached Kiyan and saw his wounds, one of which she described as "a little nick on his chest".
"I did not realise how seriously he had been injured at first."
The trial was adjourned until Wednesday.