Saul 'Canelo' Alvarez sent shockwaves through the boxing world when he tested positive for the banned substance clenbuterol in March.

The news came ahead of Canelo's rematch with unified middleweight champion Gennady Golovkin after the pair's initial bout ended in a controversial draw in September. In an entertaining 12 round clash, it was a suspect card Adelaide Byrd that ensured it finished honour's even.

Nevertheless, his positive test had called the rematch into doubt with the 27-year-old currently under investigation for a result he blames on Mexican meat. 

Golovkin had initially given a reserved reaction to the news but, rather astonishingly, let rip during a fiery interview on Wednesday.

The unbeaten fighter lamented: "Canelo's team are using these drugs and everybody's trying to pretend it's not happening.

Golovkin finally reaches his breaking point

"This guy, he knows. This is not his first day in boxing. He proves he gets benefits from everyone and he can get away with it. The commentators, commission, doping commission—this is a very bad business, [it's] not sport. Check him on a lie detector and then we can find out everything."

Big talk indeed and only time will tell whether the mega-fight will actually go ahead.

It hasn't stopped the two fighters from continuing their camps, however, with Canelo giving fight fans an update on his preparations during a series of fiery Instagram posts on Thursday.

Canelo hits back by X-rated Instagram story

He uploaded videos to his 'story' of him exercising for the fight with a series of X-rated messages for Golovkin as captions. 

The Mexican superstar penned: 'I'm gonna kick your f****** ass' and labelled him a 'little b****' - check out the posts below:

What a contrast to the calm and respectful build-up to the original fight.

The controversy over the failed test has sparked animosity between the pair and you can understand why. If Canelo is found guilty - the controversy will be unparalleled and his reputation in the sport will be cast in serious doubt.

One thing is for sure, though, 'Triple G' seriously isn't buying the Mexican meat excuse.

"Again with Mexican meat? Come on," he remarked. "I told you, it's not Mexican meat. This is Canelo. This is his team. This is his promotion. Canelo is cheating."

Canelo may have responded but as much as he promises to destroy his opponent, he might not get the chance.

Do you think the fight will go ahead? Have your say in the comments section below.