Andy Ruiz has wowed boxing fans with his incredible body transformation ahead of his upcoming fight with Luis Ortiz.

The Mexican-American stunned the world with a shock victory over Anthony Joshua in 2019 to become world heavyweight champion.

He made weight after his surprise victory at Madison Square Garden and would lose to Joshua in a rematch in Saudi Arabia later that year.

After a two-year hiatus from boxing, Ruiz Jr. returned with a points victory over Chris Arreola in May of last year.

The 32-year-old will face Ortiz in Los Angeles on Monday morning (our local time) as he looks to get back into contention for another shot at a world title.

Ahead of the fight, 'The Destroyer' shared a behind-the-scenes video that has fans in awe.

In the clip, Ruiz Jr. can be seen flexing his upper body and appears to have put on a significant amount of muscle.

"The best shape I've ever seen you in!

Motivating myself on my health journey!

Share it,” one fan wrote on Twitter.

Another added: "Best form I've seen Ruiz in."

While a third wrote: "Ruiz in that shape is a powerful punch for any heavyweight."

His opponent Ortiz enters the fight off the back of a sixth round knockout victory over former IBF world heavyweight champion Charles Martin earlier this year.

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3 More Days 👊🇲🇽🇲🇽😇😇🥊🥊🥊 pic.twitter.com/xZuCJlUCGc

— AndyRuizJr (@Andy_destroyer1) September 1, 2022