The teenager, who has not yet been formally named, died at Royal Sussex County Hospital on Friday after his family agreed that his life support should be withdrawn.
He had been in critical condition at the hospital since he was stabbed in the stomach in Old Church Road on Saturday, November 18. Flowers and messages from friends and family were left at the scene yesterday (November 25).
His death is now being investigated by the Surrey and Sussex Major Crime Team.
Jack Cunnion, 18, a scaffolder, of Essex Road, St Leonards and a 16-year-old boy from St Leonards appeared at Brighton Magistrates’ Court on Monday, November 20, charged with grievous bodily harm with intent.
They were both remanded in custody to appear at Crown Court on 18 December.