William Kadama, 14, had been on a life support machine ever since he was pulled out of the pool unconscious on 30 July.
His best friend, Gameli Akuklu, also 14, who was pulled out at the same time, was pronounced dead that day.
Lifeguard
He died of drowning, and an investigation's now being carried out to find out why William died too.
Both boys, from north London, were taking part in a summer scheme at Hendon Police Training School in London when the tragedy happened.
William's family and doctors made a joint decision to switch off his life support at Great Ormond Street Hospital.
Hear Story
Tips for staying safe
Talk about this now
