Isabel dos Santos, at one time the wealthiest woman in Africa, must surrender one of her last remaining major assets, a stake in the Portuguese energy company Galp worth an estimated $500 million, an international tribunal in the Netherlands has ruled.

In its 2020 Luanda Leaks investigation, the International Consortium of Investigative Journalists revealed that dos Santos and her husband Sindika Dokolo had obtained the stake for just a $15 million initial deposit, in a controversial deal made with Angola’s state oil company — overseen at the time by dos Santos’ father, Angola’s then-president Jose Eduardo dos Santos.

The deal “cannot be explained but for grand corruption by the daughter of a head of state and her husband,” the tribunal ruled, declaring it “null and void.” The ruling, made public last week, was first reported by Dutch newspaper and ICIJ partner, Het Financieele Dagblad.

Luanda Leaks reporting showed how insider deals, political connections and an army of Western enablers helped dos Santos amass a fortune. The exposé revealed how the billionaire and her allies benefited from lucrative deals in diamonds, telecommunications, banking and real estate.

The investigation had a profound impact on the dos Santos family. Angolan and Portuguese authorities froze dos Santos’ assets and bank accounts and launched criminal investigations. The business empire was largely dismantled.

The inside dealmaking that led to the acquisition of the Galp shares, revealed in part through leaked documents, was featured in the Luanda Leaks reporting.

In 2006, Angola’s state oil company, Sonangol, sold 40% of its interest in joint venture company Esperaza to Exem Energy, a Dutch firm owned by Dokolo. Sonangol then sold to Dokolo’s company a $99 million stake for an initial $15 million deposit. That same stake is now worth more than $500 million.

The deal was “tainted by illegality, enabling Ms dos Santos directly or through her husband Mr. Dokolo, while using her position as daughter of the Angolan President … to reap an extraordinary financial gain to the detriment of … Angola,” according to the ruling.

“This is a landmark decision,” Yas Banifatemi, one of Sonangol’s attorneys told ICIJ. “It is not something you see often that a tribunal like this recognizes embezzlement and corruption. They called a spade a spade.”

Banifatemi said that the Luanda Leaks investigation was critical to the case, making critical information public. “I’m thankful for the Luanda Leaks,” Banifatemi said. “It allowed us to fight corruption.”

In a statement, Exem Energy’s London representatives said that the company will appeal. Its attorney, Dan Morrison, noted that the panel is not a court and said that it failed to comment on Exem Energy’s evidence. “The political narrative clearly superseded the legal analysis,” Morrison said.

In separate cases related to the transaction, a Dutch court froze Exem Energy’s assets last year and removed a key dos Santos ally from the board of the joint venture company. Dutch prosecutors also launched a criminal probe into the deal. Dos Santos is also facing criminal charges in Angola.

Dos Santos denies wrongdoing and has previously claimed that legal actions against her amount to a “witch hunt.” Dokolo also denied wrongdoing. He died in a scuba diving accident last year.