KEY POINTS:
It is a family feud on the grandest of scales involving planes, palatial mansions, posh hotels, famous paintings, plus a small matter of US$40 billion ($52 billion).
Now some of Britain's top legal brains have been called in to sort it out - meaning the closely guarded details
of the falling-out between two of the world's wealthiest men are becoming public.
One is the Sultan of Brunei, supreme ruler of the tiny, oil-rich state nestled beside Malaysia on the island of Borneo. The other is Prince Jefri Bolkiah, his youngest and once-favourite brother.
Brunei's former finance minister, Prince Jefri became known as PJ to friends during his jet-setting heyday in the 1990s. Tabloids reported gold-plated toilet brushes, a Boeing 747 customised to carry polo ponies, even a gold-plated toaster in one of his cars.
The prince was founding chairman of the Brunei Investment Agency (BIA). Billions of dollars in oil revenues were funnelled by the BIA into domestic development and overseas property investments, including London's Dorchester Hotel.
And US$40 billion went into the accounts of the now estranged brothers.
Brotherly love turned sour a decade ago. Prince Jefri was accused of misappropriating about US$15 billion in BIA funds. He was fired, his funds frozen. Brunei demanded restitution. The brothers reached an out-of-court settlement in 2000. And there things stood until it began unravelling with a vengeance.
Prince Jefri claims the Sultan gave him verbal assurances that if he signed the restitution settlement he would be allowed "lifestyle" exemptions, allowing him to keep a small number of foreign properties. The BIA says there was no such deal, and that Prince Jefri has defaulted on his written undertaking to return virtually everything.
This, the London court has revealed, involves riches on a gar-gantuan scale. According to Prince Jefri's submission, he has already handed back more than 500 properties in Brunei; more than 100 properties outside Brunei, 1700 cars; five boats, nine aircraft and more than 100 paintings by famous artists.
All of which leaves the disputed properties. Prince Jefri is down to his last two homes and last two hotels: St John's Lodge, near Regent's Park in London, 3-5 Place Vendome near the Ritz in Paris, the Palace Hotel on Madison Avenue in Manhattan, and the Bel Air Hotel in Los Angeles.
Both sides have been girding for a final battle after fighting their way to the highest courts in Brunei. There, the Chief Justice ruled against Prince Jefri, rejecting the idea there had been a lifestyle agreement and telling him to comply. There was just one avenue left to the prince: the final appeal before the Privy Council in London.
The venue was a courtroom in Downing St. On the bench were five Law Lords, chaired by Lord Bingham of Cornhill, a former Lord Chief Justice.
But amid the dry legal argument, a battery of embarrassing and potentially explosive allegations and counter-allegations emerged.
Prince Jefri says the dispute arose because an agreed carve-up of BIA funds by the two men - involving "special transfers" into their personal accounts - went sour.
"The matter of special transfers is at the heart of the dispute between the two brothers," the prince's lawyers said.
"They total more than US$40 billion. It is His Royal Highness Prince Jefri's case that there was an agreement to divide up much of the monies between them. It is an agreed fact that of the special transfers that the BIA previously alleged were public money, some US$8 billion went into the private accounts of His Majesty," the lawyers added.
Far from "misappropriating" the funds, the lawyers added, Prince Jefri had used them for " ... major infrastructure projects, such as power stations and roads in Brunei". Much of the rest was for "gifts" - one of them of $62 million - "to various ministers [and] deputy ministers".
Prince Jefri's team also claimed that, given the Sultan's hold on Brunei, a fair ruling there was impossible.
The BIA's counterblast began with an insistence the Sultan's role had nothing to do with the row. He, the lawyers said, was not a party to the case. It was the BIA whose funds were at issue.
There were so many "inconsistencies" in Prince Jefri's accounts of the "lifestyle agreement", they said, that the Chief Justice had reached the only obvious conclusion: there had been no such deal.
Describing Prince Jefri as "the disgraced former Minister of Finance and chairman of the BIA", its lawyers said he was lucky to have got as good a deal as he did.
The agency had paid "roughly £100 million" to settle other parties' claims against him.
The Privy Council is expected to make a ruling towards the end of the year.
The BIA was said to be confident of its ground: a deal was a deal; the prince was trying to back out of it. The prince, said friends, was also hopeful.
"He believes he has done much good for Brunei, and feels this is an issue of fairness," one said.
A BIA statement after last year's victory in the Brunei courts made it clear they were targeting not just his homes and hotels.
"Other assets required to be transferred," it said, "include valuable assets in Malaysia, Indonesia, Singapore, the Philippines, Japan, France, the UK and the USA; works of art, jewellery, and cash ... "
- Observer