One of Australia’s richest families is fighting a supreme court siblings’ battle over the inheritance of an iron ore fortune.

Julian Wright is suing his billionaire sister Angela Bennett and the estate of his late brother Michael Wright for fraud, claiming they hid the size of the family’s true wealth and duped him out of millions in mining royalties.

It is one of the biggest fraud cases in the nation’s history and is being heard three years after Julian Wright filed an explosive writ alleging that his siblings “fraudulently misrepresented” the future value of Wright Prospecting Pty Ltd (WPPL) following the unexpected death of their father, Peter Wright, in September 1985.

Bennett is estimated to be worth almost $2bn and was labelled Australia’s fourth-richest woman in 2017 by Forbes.

Julian Wright and Bennett’s older brother, Michael Wright, bequeathed $1.2bn to his children Alexandra Burt and Leonie Baldock when he died in 2012.

At core of the case is the jarring fact that Julian Wright sold his one-third share in the family business for $6.8m in 1987 – two decades before a mining boom catapulted the company’s finances into the stratosphere.

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But as fast as the millions have rolled in, so have the legal battles.

For more than a decade, the Wright family has been in and out of court fighting each other and their former business partner, Hancock Prospecting, over shares and rights to its mining interests in the red, dusty Pilbara region of north-west Western Australia.

This latest case follows a successful claim by Julian Wright’s children, Tim and Natalie Wright, in 2008 that netted them close to $70m from their estranged uncle and aunt.

Meanwhile, the company is still mired in a years-long legal saga with Hancock Prospecting over a range of iron ore assets and royalty streams.

In his opening address to court, Julian Wright’s lawyer Pat Zappia QC claimed his client was deliberately misled by his older siblings into thinking that Wright Prospecting’s mining tenements “did not have any value”, before he made his fateful decision to sell his stake in the company.

“Immediately following Peter’s death, Michael and Angela assumed control of WPPL and together plotted to acquire all of Julian’s interests in the company and any interest that he held in Peter’s estate,” Zappia told the court.

“They did not want Julian to have any future interest in the company’s significant and highly valuable mining assets. Their objective was to get rid of him one way or another.”

Julian Wright claims Michael Wright and Bennett “trapped him like a rat in a bottle”, keeping him away from the mining business and providing only negative information about its workings.

“Matters that would otherwise have been highly material to Julian’s decision to sell were concealed from him by his siblings and those engaged on his behalf,” Zappia said.

“Those royalty entitles today are worth many, many millions of dollars and they were not disclosed to Julian.”

But Wright Prospecting denies any impropriety, arguing that Julian Wright needs to live with a decision he clearly regrets and stop retrospectively trying to undo binding agreements.

The firm’s senior counsel Kristina Stern called for the case to be dismissed on Thursday and for costs to be awarded against Julian Wright.

“The evidence falls well short of proof of fraud,” Stern said.

“There is no evidence of misrepresentation or concealment on the part of Michael Wright or Angela Bennett.”

Stern referred to a previously submitted signed deed, which she labelled “utterly fatal” to Julian’s case.

The deed was part of the 2008 legal settlement between Bennett, Michael Wright, Julian Wright and his two children. It contains a pledge that the siblings would not bring further legal action about the family inheritance.

The warring siblings owe their immense wealth to their late father, Peter Wright, who together with school buddy and business partner Lang Hancock, signed three agreements in the 1960s, carving out a river of royalties that still flows today.

Both Hancock and Wright are patriarchs of Perth’s richest mining families and are credited as pioneers of WA’s lucrative iron ore industry.

Hancock’s daughter, Gina Rinehart, who has also previously been embroiled in legal battles with immediate family, is Australia’s richest woman, worth $15.2bn according to Forbes.

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WA is the world’s largest supplier of iron ore. Most of the metal extracted is sold to China to be turned into steel, according to the WA Department of Mines, Industry Regulation and Safety.

Australia’s decade-long resources boom can be credited to a once-in-a-century explosion in construction projects in China that saw iron ore prices skyrocket by a factor of 10 in the early 2000s.

Families like the Wrights and Hancocks became billionaires as a result.

The boom may have waned but iron ore is still big business in WA. Iron ore sales reached a record 790m tonnes and were valued at $63bn in 2016 to 2017, according to the state government.

While WPPL does not mine the ore, it brokered an ongoing royalty deal with mining giant Rio Tinto.

But according to Zappia, a statement of assets lodged as part of the processing of Peter Wright’s will in April 1986 did not detail this massive royalty agreement over WPPL’s Pilbara mining interests.

“That asset was not disclosed to Julian,” Zappia said.

The defence claimed to have documents refuting Julian Wright’s claim that he was kept in the dark about potential mining royalties. Stern said there was evidence that Julian Wright was aware of his father’s involvement in previous legal proceedings relating to a royalty dispute.

The case continues.