Why is a UFC star fighting a boxer?

A pertinent question.

The undefeated Floyd 'Money' Mayweather will face UFC icon Conor McGregor in a boxing match which is already being described as 'The Fight of the Century' - but you would be forgiven for asking 'great, but why?'

Each men will have their different reasons for taking the fight, but the huge sum of money both fighters stand to make will be a considerable motivation.

It's estimated that the two could earn as much as $100m from the bout, although it's generally accepted Mayweather will receive a greater share of the fight purse given his superior reputation as a professional boxer.

Both fighters are renowned for their showmanship and the opportunity to earn a multi-million dollar paycheck was too good to ignore.

Both fighters have, arguably, achieved all they can in their respective disciplines.

Floyd Mayweather remains unbeaten in his career, winning 49 fights with 28 of those coming by knockout.

Why has McGregor come out of retirement?

Well technically he never officially retired from UFC. McGregor causes a huge furore when he posted a short statement on Twitter, appearing to announce his retirement.