On December 7, Andy Ruiz Jr and Anthony Joshua will once again share the ring as the Mexican puts his heavyweight titles on the line.

In what was one of the biggest upsets in boxing history earlier this year, Ruiz Jr managed to claim all of AJ's belts and stop him for the first time in his professional career.

Joshua had gone through the likes of Wladimir Klitschko, Dillian Whyte, Joseph Parker, Alexander Povetkin and Carlos Takam, but he simply didn't have an answer for Ruiz Jr.

What made the result even more shocking was the fact that Ruiz Jr shouldn't have even been in the ring! It should have been Jarrell Miller, who failed numerous drug tests and lost the right to fight for the belts.

It was supposed to be a walk in the park for AJ. It was supposed to be his coming of age in America. It ended up being a nightmare.

The 'chubby' boxer who ate Snickers and was just happy to be sharing the ring with the British superstar became the heavyweight champion of the world and the face of the division.

However, fast forward a few months and a whole lot has changed.

Ruiz Jr is now well known around the world and is living his life like a heavyweight champion, but he's also clearly been working hard in the gym ahead of the rematch.

Everyone made comments about Ruiz Jr's physique ahead of the initial fight. People were calling him fat, out of shape and were comparing his body to that of Joshua's.

Now, however, the Mexican is starting to look the part.

Below, the picture on the left is Ruiz Jr earlier this year. The picture on the right is him now.

A quite incredible difference, is it not?

This new image shows just how good Ruiz Jr is now looking, and it's clear to see he's been working hard for the rematch.

If Ruiz Jr was 'out of shape' for the initial fight, which he won, who knows what he could do when he's in shape and had months to prepare for the bout.

All questions will be answered in December.