This week's ruling followed a four-year legal tussle which exposed ugly and deep-seated family divisions, the whole affair playing out in public despite Rinehart fighting tooth and nail to have the proceedings suppressed.
In emails released last month, Hancock repeatedly referred to his mother as "Fat" and "Fatty". "Fat would have quickly grown tired of supporting your shopping and leisure activities," he wrote to Bianca, whom he joined in the family trust case.
Another sister, Hope Rinehart Welker, was originally part of the action, too, but settled with her mother for A$145 million after complaining of being "down to my last A$60,000". Rinehart's youngest daughter, Gina, sided with her in the family feud.
If Hancock was insulting about his mother, she was hardly complimentary about her three eldest offspring, describing them as "lazy" and "spoilt".
In one statement, she declared: "[They] have enjoyed very privileged lives ... private schooling, private tutors, private summer schools, extensive holidays overseas, designer clothes, private health care, expensive jewellery and watches ... multi-million-dollar homes with water views and swimming pools."
Another exchange of correspondence - between Hancock, who lives in Thailand, and Jay Newby, company secretary of Rinehart's Hancock Prospecting - seemed to confirm that view. In the emails, Hancock bragged about his luxury villa, complete with water slide. Newby referred to it as "your Thai palace".
The trust, estimated to be worth up to A$5 billion before mineral prices began to plummet, was set up by Rinehart's father, Lang Hancock, who discovered vast iron ore deposits in Western Australia's Pilbara region.
His four grandchildren were the beneficiaries, and the trust was due to vest in September 2011, on Gina's 25th birthday. Unbeknown to them, Rinehart changed that date to 2068, later explaining that they would otherwise have been bankrupted by huge bills for capital gains tax.
That claim was rejected by Judge Paul Brereton, who also found that Rinehart had repeatedly tried to pressure her children into dropping the case, using "influential connections" and tactics "which closely approach intimidation".
Embarrassingly for the federal Government, those connections included Rinehart's close friend Barnaby Joyce, then a National Party senator, now Agriculture Minister, and a now retired Liberal MP, Alby Schultz. Both men wrote to Welker, with Joyce urging her to keep the affair "in house".
Rinehart also tried to enlist Olympic swimmer Grant Hackett, who used to be in a relationship with Bianca.
On ABC radio yesterday, Hancock excoriated Joyce for effectively "pushing her [Welker] to drop the case", describing his behaviour as "outrageous" and "a dangerous example of a senior politician prepared to jump off a cliff without checking for rocks below".
He also expressed certainty that his mother would appeal against the ruling, saying: "Every decision along the way she's appealed all the way to the High Court. So I can't see this being any different."
Yesterday, Bianca described her appointment as trustee as "a significant step towards restoring family harmony".
In the separate case, which returns to the Federal Court next month, Hancock and Bianca have accused Rinehart of misleading and deceptive conduct in relation to their share of the profits from her iron ore projects.
