Sergey Kovalev opens up to Yahoo Sports about his eighteenth professional fight against Roman Simakov, which ended in tragedy.

Ahead of his latest World Title defence against Isaac Chilemba, ‘Krusher’ explains how after a break from the game how he decided to continue.

Former trainer Abel Sanchez and the unbeaten Russian puncher relive that night back in December 2011.

Watch the ten minute documentary below (Contains scenes that some viewers may find upsetting)