Fans stunned by Andy Ruiz Jr's incredible body transformation, he now has a six-pack

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

Ruiz Jr stunned the world with a shock victory over Anthony Joshua in 2019 to become heavyweight world champion.

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

After a two-year break from boxing, Ruiz Jr made his comeback with a points victory over Chris Arreola in May of last year.

The 32-year-old Mexican-American next faces Ortiz in Los Angeles on Sunday as he looks to work his way back in contention for another world title shot.

Ahead of the fight, 'The Destroyer' shared a behind-the-scenes promotional video of himself which has stunned fans.

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

He even looks to have a six-pack, with fans on social media blown away by his appearance.

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

— AndyRuizJr (@Andy_destroyer1) September 1, 2022

"Best shape I've seen you in! Motivating for myself on my health journey! Crush it," wrote one fan on Twitter.

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

While a third wrote: "Ruiz in that shape is a handful for any heavyweight imo."

His opponent Ortiz, 44, heads into the fight on the back of a sixth-round TKO victory over former IBF heavyweight world champion Charles Martin earlier this year.

Wow you look in shape fella!

— Mr Wingless (@MWingless) September 1, 2022

Best shape I’ve seen you in! Motivating for myself on my health journey! Crush it! 💪🏽

— Chris (@YoungAssDad) September 1, 2022

Crazy right!? Dude has a 6 pack almost. Insane change from the last Joshua fight to now.

— Fau1in (@fau1in) September 1, 2022

But he has fought just twice since losing to former WBC champion Deontay Wilder in 2019, with his only other bout ending with a victory against Alexander Flores in 2020.

Speaking earlier this week, Ruiz Jr said he expected his clash with Ortiz to be one of the most physical fights of his career.

"Yeah it is, because it's a style that I haven't fought before, you know?," said Ruiz Jr.

"But like I said, I like taking chances and I feel like I perform better when I'm under pressure.

"On Sunday it's gonna be a hell of a fight, but I know I'm gonna get that victory."