The brother of billionaire iron ore heiress Angela Bennett has suffered a legal setback on the eve of a Supreme Court trial where he has accused her of fraud and is seeking to recoup a huge piece of the family's vast fortune.

Perth businessman Julian Wright alleges Ms Bennett and their deceased brother Michael Wright duped him out of a one-third stake in Wright Prospecting and decades of iron ore royalties after the death of their father Peter Wright in 1985.