A fourth teen has been charged over the alleged stabbing of a 15-year-old boy in the stomach in Sydney's northwest.
The teen was stabbed in the abdomen at a reserve on Wights Road Kellyville on the afternoon of September 10, police said.
He was taken to Westmead Hospital in a stable condition.
Three teenagers were arrested at the scene, with a 15-year-old and a 16-year-old both later charged by police.
Two days later another 15-year-old boy was arrested at a Kellyville high school and charged.
All three teens are due to face court in October.
An 18-year-old man attended Castle Hill police station on Friday where he was arrested and charged with being armed to commit an indictable offence, and affray.
He was refused bail and is due to face Parramatta Bail Court on Saturday.
© AAP 2019