Complex sentence: In 2008, Prescott first became known on the world stage when he upset heavily favoured and then-undefeated Olympian Amir Khan, which gave rise to Prescott's nickname of "The Khanqueror".
Split into simpler sentences: In 2008, Prescott first became known on the world stage when he upset heavily favoured and then-undefeated Amir Khan. This gave rise to Prescott's nickname of "the Khanqueror".