'It pained me leaving Arsenal for Crystal Palace - now I'm worth more than their entire squad'

This former Arsenal star admits it was hard facing the Gunners for Crystal Palace but the player is now worth a staggering £10billion

Former Arsenal midfielder Mathieu Flamini was pained after leaving the Emirates Stadium for Crystal Palace in 2016. But the Frenchman is now a billionaire after founding a successful green chemistry company.

The Gunners are Premier League champions once again and they'll end their crowning campaign with a trip to Selhurst Park on Sunday. A Champions League final also awaits Mikel Arteta's side. Flamini played for both clubs during a stellar footballing career and left north London for south of the capital when he joined Palace in 2016.

However, having founded GF Biochemicals, a green chemistry company focused on finding sustainable alternatives to oil-based products, in 2008, Flamini now has a net worth of £10billion, more than 10 times the cost of Arsenal's title-winning squad.

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Flamini first signed for Arsenal in July 2004, the summer after their Invincibles season, and spent four years under manager Arsene Wenger before joining AC Milan. After his deal with the Italian side expired in 2013, he headed back to his former club.

The French midfielder's second spell lasted until 2016, when he signed for Palace on a free transfer. That season, the Eagles beat a struggling Arsenal 3-0 and Flamini admitted it was hard to see his old club in such turmoil.

As fans continued to protest against manager Wenger, who would leave the club the following season, Flamini said: "It is painful because I am still an Arsenal fan. But it is not an easy situation. I had some amazing times with Arsene Wenger.

"He did so much for myself. It is difficult for me to comment from the outside what is happening with Arsenal. Results are not what they want, that is for sure. I saw Arsene. Of course, everyone is disappointed. When you are a big club you want to win every game, so that is normal."

Flamini retired two years later after a short spell with Spanish side Getafe and focused all of his efforts on GF Biochemicals. He also funded the company's rigorous research and development for years during his playing days, but kept it a secret from team-mates.

His company became the first in history to mass-produce levulinic acid, a green alternative to petroleum, and quickly became a multi-billion-dollar success. The molecule his company produces is hailed as a holy grail because it can reduce the carbon footprint of everyday household products by up to 80 per cent compared to traditional petroleum.

Flamini, the CEO, holds a 60 per cent stake in the business and therefore his fortune has rocketed to an estimated £10billion. This figure dwarfs the amount the Gunners spent constructing their squad, which has just been crowned Premier League champions, an estimated £780million.

Speaking to Harvard Business Review, Flamini said: "Football is a team sport but performance remains individual. As a player, you are judged on your own results. As a business leader, your role changes completely: you become a coach. The team comes first, and you are judged by your team's performance.

"Admittedly, I had to adapt, but there are many parallels between top-level sport and entrepreneurship: you need to know how to handle the pressure, be resilient, determined yet patient, and not be afraid of the workload or the sacrifices…

"We launched over 10 years ago, but our first product has only recently been brought to market. It is therefore a long-term investment that requires patience. Team spirit is also essential for overcoming difficulties. As a leader, you need to be a good listener while remaining clear about the vision and objectives."