Geomancer Tony Chan Chun-chuen, 49, claims a 2006 will leaves him as the sole beneficiary to the multibillion-dollar estate of the late Chinachem tycoon, who was known as "Little Sweetie" because of her trademark pigtails.

But yesterday it emerged that the rival claimant - the Chinachem Charitable Foundation - has a report from an international handwriting expert who claims Nina Wang's signature on that will is a fake. The expert is said to have studied 80 of the billionaire's signatures dating from 2003.

But in echoes of the bitter tussle over the will of Nina's husband, Teddy Wang Teh-huei - in which arguments raged over forged signatures - Chan's lawyers said they have also engaged a handwriting expert, Dr Audrey Giles, to assess the contested will.

Speaking outside the pretrial hearing at the High Court, Chinachem Charitable Foundation lawyer Keith Ho Man- kei said: "We have evidence to prove that [Chan's will] is false. We have an expert report from Robert Radley. He is a handwriting expert from the United Kingdom."

Earlier in court, Chan's lawyers expressed dismay at the apparent change of tactics.

Chan's barrister, Ian Mill QC, said up until yesterday the focus of the hearing had been on whether Wang was under undue influence and whether she was in a state of adequate mental capacity at the time she allegedly signed the will leaving all her assets to the fung shui master.

Now, however, Mill told Judge Johnson Lam Man-hon, the foundation seems poised to challenge the authenticity of the signature and to plead a case of fraud. "We have very serious concerns of raising such serious allegations at this point," Mill said.

The foundation holds a 2002 will that bequeaths Wang's assets to the charity and her loved ones. The validity of this will has never been in doubt.

Judge Lam will hear the foundation's plea amendment application on April 14.

Lam has also ordered the foundation to disclose the identity of an anonymous witness by Friday if it plans to use him during the hearing. According to the Straits Times, the witness is Singaporean and an executive with investment firm Goldman Sachs.

Separately, records kept by Nina Wang's personal assistant up to her death are expected to be part of the foundation's evidence.

The pretrial hearing was adjourned until Friday morning, when the court will consider applications to alter witness statements and expert reports, as well as requests to extend the time available to study them.

The dispute over the will began after Wang's died on April 3, 2007, aged 69. She became one of Asia's richest women during the final years of her life, thanks to her husband's vast business empire which he started building in the 1960s.

Following Teddy Wang's kidnap in 1990 and presumed death in 1999, Nina Wang and her father-in-law, Wang Din- shin, engaged in bitter legal battles over his estate.

Nina Wang was at one point charged with forgery but the Court of Final Appeal ruled in 2005 that she was the rightful beneficiary of her husband's estate.