John Hancock has made a shock appearance at Western Australia’s Supreme Court amid a multibillion-dollar court battle over his family’s mining riches, declaring he had flown to Perth to defend the reputation of his grandfather, Lang Hancock.

Mr Hancock and his sister, Bianca Rinehart, were seated together in court on Monday as lawyers for the pair made the extraordinary claim that Hancock Prospecting’s entire stake in the Hope Downs mining operation should belong only to Lang Hancock’s four grandchildren, and not their mother, Gina Rinehart.