David Beckham, Mark Wahlberg and when a celebrity brand deal goes really wrong.

A simple Google search for F45 brings up the company's website as the top result, where they promise to transform your life. However, for David Beckham, that promise turned into a costly ordeal.

Beckham is suing actor Mark Wahlberg for allegedly misleading him into endorsing the fitness brand.

According to Beckham, the deal left him $16.4 million out of pocket after he agreed to be the firm's global ambassador upon moving to Los Angeles in August 2021.

The former footballer is also suing the actor's firm, Mark Wahlberg Investment Group (MWIG), and the founders of F45, Adam Gilchrist and Rob Deutsch.

Watch: Victoria Beckham thirsts over David Beckham. Post continues below.

He alleges that he suffered a loss exceeding $16.4 million AUD when the stocks he was promised were withheld until after the share prices had dropped significantly. 

Meanwhile, Wahlberg's lawyers denied the claim, calling the "fraudulent conduct" accusations baseless in a motion to dismiss.

"The 209-page, 610-paragraph SAC [complaint] tries to make up with length what it lacks in merit," read the response from Wahlberg's lawyers.

Functional 45 (better known as F45) is the worldwide Australian-born exercise phenomenon that went from Sydney to New York, opening up thousands of franchises and proving to be an extremely profitable business.

Wahlberg, who has over 30 per cent ownership of the company, holds the position of chief brand officer. However, the company was co-founded in 2011 by Sydney bankers Deutsch and Gilchrist. 

It was based on a simple idea — to modernise the traditional gym format with a 45-minute high-intensity, group workout.

Beckham is suing Wahlberg and his investment firm, claiming he lost $16 million after agreeing to endorse the company. Image: Instagram.

At the time, the concept was revolutionary. Within the first two and a half years of operation, the fitness chain went from one gym in Paddington in Sydney's eastern suburbs to around 200 studios. 

In less than eight years, it went on to sell over 2,000 franchises across 63 countries.

But as soon as the pandemic rolled around in 2020, the fitness franchise experienced a sudden shift.

Unexpectedly, the revenue and share price took a hit. Then, Deutsch stepped down as the company's CEO just as F45 was set to go public and make its debut on Wall Street.

"As the founder of F45, I’ve had the privilege of helping build the company into one of the fastest-growing fitness franchises in the world. My time at F45 has been deeply rewarding and enjoyable. I am incredibly thankful for the business partnerships and friends made along the way," Deutsch wrote on Instagram.

"As some of you know, I recently (two months ago) transitioned out of my role as CEO at F45. I still remain a shareholder. The F45 future is bright, and I look forward to watching from afar. I look to the future with optimism and wish all friends, family, and franchisees a safe journey through this challenging time."

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A post shared by Rob (@_rob_deutsch_) will meet again soon in the wellness space.. BE SAFE and THANK YOU for the support."

Off the back of his departure, the company went ahead with their plans to go public, appearing on the New York Stock Exchange with a $2 billion valuation.

But while the company had huge plans to expand internationally, things took a disastrous turn.

Since hitting the public market, F45's stock price plunged, with the brand experiencing a significant decline from its debut price, dropping 88 per cent. 

According to the Financial Review, F45 told investors it had secured a $US250 million (roughly $350 million AUD) line of credit that it would extend to franchisees to help hit its target of opening 1,000 new studios in 2022.

However, it was then revealed that the credit line would not be available. 

Gilchrist announced he was stepping down as F45’s chief executive and chairman.

The company also shared that it would be laying off 110 staff "amid changing macroeconomic and business conditions". 

After the dramatic stock price plunge and staff cuts, Deutsch shared his reaction on Instagram, writing: "Never in my wildest dreams could I have imagined this." 

"When I exited and sold out of F45, I left a healthy, phenomenal, beast of a business. All the way from the company culture to the heartbeat of the business… The workouts. F45 was special," he said.

"I genuinely hope all of the 110 laid-off staff, find happiness and opportunities elsewhere."

Despite the turmoil and massive losses, F45 executives are confident the fitness empire will survive, however, after suffering another blow thanks to Beckham, only time will tell.

Feature Image: Instagram.