Rupert Murdoch knows there are a few advantages to owning a global media behemoth: you get to control the news.

So when the Melbourne-based Crikey website posted a rumour on Monday that Murdoch had split with his third wife Wendi Deng, what would normally rate as front-page news barely made a blip on the media radar.

''The first I heard of it was when I read it online,'' Murdoch's Sydney spokesman Greg Baxter told PS this week, adding he had no comment to provide, unable to confirm or deny the rumour. A subsequent email to Murdoch's New York office on the subject predictably disappeared into the ether, failing to clarify the status of the 10-year marriage.

''It's the oldest trick in the book,'' Murdoch biographer Michael Wolff told PS from New York. ''They [the Murdochs] never deny anything because they know it will just inflame it regardless of whether it is true or not.''

So was it just a coincidence that Murdoch's mother Dame Elisabeth, who celebrates her 101st birthday in eight weeks, cancelled a series of interviews promoting her open garden at the family's Cruden Farm this week? Dame Elisabeth and her daughter-in-law have had a challenging relationship over the years, and quite publicly so.

The original Crikey item claimed ''senior News Corporation figures in the US'' were ''openly discussing'' that Murdoch and Deng had separated.

''If Wendi has left Rupert that means there will be two less children to be pushed into the inheritance pot joining four from his first two marriages,'' Crikey claimed. However Wolff, who had unprecedented access to Murdoch, his family and closest associates for his biography The Man Who Owns The News, disagreed.

''That is simply not true. The trust is already set up. Wendi's children, Grace and Chloe, have an economic participation in the trust along with the adult children and that's not going to change,'' Wolff said.

The Murdoch trust, which holds most of the 78-year-old's $US4 billion assets, has been a sticking point for years within the family. Murdoch's previous wife Anna agreed to a $US100 million divorce settlement after 32 years of marriage, despite potentially being entitled to much more, after Murdoch agreed to limit participation in the trust to his four adult children. That changed when he married Deng in 1999 (17 days after divorcing Anna), striking a deal with each of his adult children, reportedly worth $US150 million apiece, to allow the girls into the trust.

Wolff said rumours of the couple separating were a common occurrence without much grounding.

''I have spent a fair amount of time with Wendi and everything she said sounds like someone who is quite happy with their position in life, but again, who knows what happens inside a marriage?'' Wolff said.

''There has always been a whispering campaign, partly because he is 40 years older than she is and nobody can imagine Rupert having sex. A lot of people don't like Rupert and it might have something to do with her being Chinese ¡­ all of those factors which can become combustible.''

However Wolff admitted that since his book was published last year his relationship with the Murdochs has become decidedly frosty and he has not seen much of them.