Amro was a British national whose family originated from Egypt
A 14-year-old boy died in west London after his throat was slashed by a friend, police have said.
Amro Elbadawi, from West Kilburn, was injured in Dart Street, Queen's Park, on Thursday. He died in hospital.
Police said a 16-year-old arrested on suspicion of Amro's murder was a "long-standing" friend of the victim.
Det Supt Colin Lee said one line of inquiry was that Amro died after a play fight went wrong. A knife has been recovered from the scene.
Amro, a British national with family originating from Egypt, was fatally injured as he walked home from the Paddington Academy school in Queen's Park on Thursday evening.
He staggered into a nearby health centre where a council employee cradled him in her arms as they waited for an ambulance. He died in hospital an hour later.
Det Supt Lee said the boy's family was "distraught" and added: "This has been a terrible, terrible shock for them."
He added: "We would appeal to people: 'Do not carry knives'."
Up to 100 youths gathered at the area of the incident on Friday, where floral tributes were left.
One message read: "To the best boyfriend in the world (Amro). I miss you and love you."
Online tributes described Amro as a member of the SD Crew, also known as Street Disciples or Street Dreamz. One message said Amro's nickname was "Lionheart" and another message read: "RIP Amro, I love you to bits, I won't 4get u."
The head of Westminster City Council's youth service, Sharon Cohen, said two of her staff saw the incident "between two young people who were friends".
"From what young people tell us there is no suggestion this was gang related or pre-meditated," she said.
"The sad reality is that if you carry a knife there is the real danger that the pettiest of teenage disputes can all too quickly turn into a tragedy."
Paddington Academy principal Phil Hearne said staff were "deeply saddened" by Amro's death.
"He was a student in Year 10 studying for his GCSEs and will be greatly missed," Mr Hearne said. "Our thoughts and prayers are with his family."