Millions tuned in to see KSI beat Joe Weller in the biggest amateur boxing match of all time. But what didn't they see? The blood, sweat and determination underpinning KSI's intense training regime and a revealing look at his world off camera. This is the exclusive and never before seen story of Knowledge, Strength and Integrity, and how JJ, with 18m YouTube subscribers, went from actor to athlete.

• Documentary