Julian Wright, the third child of Lang Hancock's business partner Peter Wright, is suing the estate of his late brother Michael Wright and sister Angela Bennett, alleging he was not told about Wright Prospecting's potential.

He sold his share in the company for $6.8 million in 1987.

Wright Prospecting partnered with Hancock Prospecting to pioneer the Pilbara iron ore industry and is now worth billions of dollars.

Mr Wright testified on Wednesday that in the early 1980s he lost money trading bank bills, admitting he "got the market wrong".

He said his father then agreed to lend him $30,000.

"I was summonsed and we had a family meeting," Mr Wright told the WA Supreme Court.

"He was furious and critical, and I could hardly get a word in.

"He just tore strips off me."

Mr Wright said his relationship with his father deteriorated after the "bank bill incident" in 1982.

He said he left the company, as planned, at the end of June 1983 and he had no further involvement in it, although he remained a director and shareholder, but never attended a board meeting or received any financial reports.

But last week, a lawyer for Mr Wright's siblings told the court he had been an active board member and they did not conceal anything.

Their father died overseas in September 1985.

Central to Wright Prospecting's argument is Mr Wright's action being "utterly fatal" because a settlement in 2008 saw his children receive $70 million and included an agreement he not sue his siblings over the will.

Mr Wright's testimony continues.

Australian Associated Press