The juvenile from HMP Feltham A, which holds children aged between 15 and 18 who are on remand or have been convicted, died in hospital on Monday.
A Youth Custody Service spokesperson said:
“We were saddened to hear of the death of a child from YOI Feltham, who died in hospital on Monday 20 April, and our thoughts are with their friends and family.
“As with all deaths in custody, the Prisons and Probation Ombudsman will investigate. It would be inappropriate to comment further at this time.”
A Met Police spokesperson said:
“On Tuesday, 21 April at 00:05hrs, police were notified by staff at Feltham Prison and Young Offender Institute about the death of a boy who had been found unresponsive and later died in hospital.
“The London Ambulance Service were called at around 21:30hrs on Monday, 20 April and treated the boy, aged 16, before taking him to hospital. He sadly died at 23:43hrs.
“At this stage, the death is being treated as unexpected. A post-mortem examination is scheduled for Friday, 24 April. Officers are working at pace to establish the full circumstances and are pursuing all lines of inquiry.”
