Mr Robinson is locked in a legal battle with Dr McCullough's executors and a US university over her estate, which is estimated to be worth millions of dollars thanks to her art collection and royalties from her 25 books, including the 1977 hit The Thorn Birds.

The NSW Supreme Court has heard there are at least two wills circulating. The first was signed in Sydney in July 2014 and sets out why Dr McCullough had decided not to make Mr Robinson, her husband of 30 years, a beneficiary of her estate.

On the same day, she signed a "Bequest Intention Letter" in favour of the University of Oklahoma, making it the sole residuary beneficiary.

But three months later, the will was amended so that the name University of Oklahoma Foundation Inc was removed and replaced with Mr Robinson's name. As a result, he became the sole beneficiary.

In a statement of claim the university claimed Dr McCullough did not amend the will of her own volition. It says by that time, Dr McCullough was in such poor health, including blindness, that she was totally reliant on and under the influence of her husband.

In an amended statement of claim, the estate's executor, literary agent Selwa Anthony, replaces the university as the plaintiff. She continues the claim that the July 2014 will is in fact Dr McCullough's last will and testament.

In his defence, Mr Robinson says the July 2014 will is not valid and in any case, it was replaced by yet another document signed on her beloved Norfolk Island in January 17, 2015 about a fortnight before her death from a series of strokes.

Alternatively, he says the July 2014 document was torn up or destroyed by Dr McCullough – or by someone else at her direction – with the intention of revoking it.

In a cross-claim, Mr Robinson asks the court to grant probate over the January 2015 will. However, he says if the court does not agree, there is another will, dated 2005, that should be considered to be her true testamentary intention. This will was also signed in Norfolk Island and Mr Robinson is the sole executor.

Dr McCullough was an honorary founding board member of the University's Board of Visitors at its College of International Studies where she regularly mixed with heavyweights of the world stage.

Guy Patton, president and chief executive of the University of Oklahoma Foundation, which handles gifts to the university, told Fairfax Media in June last year that Dr McCullough always intended to leave her estate to the university.

Dr McCullough's weighty series of books about the Roman empire won her much academic kudos. That series is believed to have brought her to the attention of academics at Oklahoma University and in 1997 she was invited to speak at its first foreign policy conference.

But Mr Robinson's lawyer John Brown was adamant that Dr McCullough intended to leave her estate to her widower, an original descendant of the Bounty mutineers.

The matter returns to court on June 20.