The story was headlined "The business divorce of the century". The assumption was that the Murdoch split - whether amicable or vitriolic - would change the face of one of the most powerful and certainly one of the most intriguing media empires.

But Anna Murdoch's decision to turn the heat up and file for divorce in a Californian courtroom called for a new heading. If Kelvin MacKenzie had been editing on the night, the outsized headline would have screamed: "Gotcha!" For Mrs Murdoch has forced her husband on to the ground he most fervently shuns: public disclosure.

It was a calculated stratagem. The prospect of Murdoch having to unravel the intricate multi-billion web of interests that makes up News Corporation in the glare of publicity had the media world agog with anticipation.

The international tax authorities must have been pretty excited, too. For years they have been frustrated in their attempts to get Murdoch to pay a proper amount of tax, unable to unravel cross-company financing deals stretching to holding outfits parked safely in offshore havens like the Netherlands Antilles, the Cayman Islands and Bermuda.

This £18 billion business last year notched up £800 million of operating profits only to pay £62 million of tax, a rate of less than 8 per cent.

Investors who have called for Murdoch to put a value on his main assets will also have been intrigued. Would the floating off of 20 per cent of Fox, the company where Murdoch's huge US film and TV interests are lodged, be delayed or scrapped? Or would they be speeded up to help put a value on the couple's joint wealth?

Certainly, as the avalanche of media attention began to cascade, Anna was in no hurry to help. The divorce petition said Mrs Murdoch was "unaware of the full nature of the. . . assets and obligations. . .and [would] amend this petition after discovery or at trial."'

She knew how to make the threat of such disclosure really sting. If she did not know the details, who the hell did? The trouble, of course, is that it is very unlikely that this divorce will ever go to court. Anna Murdoch and her lawyers know that, as do Rupert and his legal advisers. This is a ruse to wring a settlement out of the man - known for his personal parsimony - by hitting him where it hurts most.

As one Murdoch watcher put it: "There is no way details of Rupert Murdoch's personal holdings in his business empire are going to be aired in a public court, nor even in private divorce proceedings. This is a ploy to get a better offer."

The received wisdom among people close to this inscrutable dynasty is that Murdoch has already made one offer - presumably not as large as it could have been - to his wife of 31 years. The expectation is that, in pretty short order, perhaps in the next few weeks, there will be a second one that better fits the bill.

By threatening a high-octane, public divorce case, Anna Murdoch is making it less likely that there will need to be a third or a fourth offer before the clincher is reached.

The rival press empires eager to pick over the emotional and financial entrails of Murdoch's life are likely to be disappointed. Instead they may have to satisfy themselves with reporting the fact of a very generous but actually not very illuminating divorce settlement.

It will put a value on the Murdochs' many properties in Sydney, Aspen, London, California, the jet, the cars, the jewels and the art. And it will put a nominal value on the worth of the business by pricing Anna's share of an empire built up over more than 30 years of, until now, loyal partnership.

But it will be a phoney value, privately agreed and not a recognised business valuation. It will not explain how Murdoch funds losses at the Times to pay for the price war or how he keeps his tax bill low, or how he will pay for his grand plans to dominate the world of digital television.

One suspects that this is the way all the Murdochs - Anna included - would prefer it to be.

The story of this extraordinary partnership and its demise is one of tidal dynastic ambitions and fierce and binding loyalties. The Murdochs have managed a spectacular feat. They operate in perhaps the most un-private world of all, yet manage to remain incredibly discreet, not least because they control vast swathes of it.

It is surprising that we don't know more. We know that the media world is littered with people who have risen and fallen in the Murdoch empire. People elevated to the very heights of trust and influence only to be cast aside to nurse bitter grudges. Yet few have sought public vengeance.

The family does not exactly hide away. The father, the mother, and the eldest son Lachlan are main board directors. The daughter Elisabeth, BSkyB's general manager, and youngest son James, head of multimedia in the US, are all high-profile public figures in the firm. The three children are all contenders to inherit the throne. But, in reality, what do we know about these people? The answer is: little more than the very little they want us to know.

We knew that for several years Anna had been trying in vain to persuade Rupert to slow down. Her equally unsuccessful attempts to persuade him into a few cultural pursuits like opera were also allowed to get out. The fact that she was uncomfortable about the way he pits their children against each other in a race to test who will succeed him was also given an airing. All these snapshots were released by her to put the pressure on.

They did not work. Murdoch remains fixated by work, is happy to be portrayed as a bit of a philistine, and his children are still vying for ultimate control - even if Lachlan looks like pipping his sister to the post.

Murdoch himself has let the odd thing slip. Most recently in Mathew Horsman's book, Sky High, he revealed that he was uncertain about Elisabeth's commitment to the cause and that all the voting rights over the family's holdings in News Corp - a 31 per cent slug valued at more than £3 billion - had been put in the children's names, a piece of information that most public companies would have been obliged to disseminate officially and immediately.

When the news of the separation came it was in the gossip column of the New York Post, one of Murdoch's own papers. The columnist spoke of how the decision to split was amicable, but had left the couple "torn'. Business continuity was ensured, though, because Anna would remain on the News Corp board.

Like most things in the Murdoch world, the announcement read like a rehearsed scene in a well-plotted drama. It would be too conspiratorial to suggest that the marriage collapse was that carefully scripted. But the fact that the mother and father relinquished the voting rights to the family shares well in advance of the split perhaps suggests the marriage died after a slow deterioration rather than suddenly and that the continuation of the empire was on everyone's mind.

What has happened since is hard to know. There is tittle-tattle; there are, for instance, murmurs of divisions between the children, with the daughter said to be arguing that her mother has been hard done by. And the extreme course of events last week suggests that Anna is aggrieved about more than just workaholism.

But the fact remains that, for all the apparently visceral impulses that drove Anna Murdoch to threaten a war in public, this is a family where business comes first.

That means two things. That the price for Murdoch of seeing that business survive in something like its current shape will be one of the most expensive divorce settlements ever recorded. The settlement, however, will be reached out of court.