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A boy was found dead in his prison cell when staff went to check on him in the morning.
He was found unresponsive in his cell in Cookham Wood Young Offenders Institution, Rochester, at 6.40am on Saturday.
A Prison service spokesman said: "Staff attempted resuscitation and paramedics attended but he was pronounced dead at approximately 8am."
His next of kin have been informed and his death is not being treated as suspicious.
The spokesman added: "Every death in custody is a tragedy and we always seek to improve our procedures for caring for prisoners, including young offenders, where possible.
"As with all deaths in custody there will be an investigation by the independent Prisons and Probation Ombudsman. Additionally, as he was under the age of 18, there will be a Serious Case Review commissioned by the Local Safeguarding Board."
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