Victoria's Cancer Council is suing a woman's $13 million estate to force them to hand over her medical records to make sure she was of sound mind when she rewrote her will that cut out the not-for-profit organisation.

Elizabeth Bell Thomson, from Melbourne, had bequeathed her whole estate to the council back in 2004 if her husband, Kenneth, was to die before her.

But she had another will drawn up in 2011 and this one excluded the council and her husband.

Victoria's Cancer Council is suing a woman's $13 million estate to force them to hand over her medical records to make sure she was of sound mind when she rewrote her will

Ms Thomson, who died April last year at the age of 94, decided to leave her $12,660,555.81 estate to executrix Victoria Anne WIlshire and second cousin Peter Gordon Jeffs.

The elderly woman also left a relatively small gratuity of $500 each to the RSPCA and the William Angliss Hospital, where her husband was being cared for.

Before her death, Ms Thomson was moved to Melbourne's Domain Gracedale Aged Care after she developed glaucoma, visual impairment and dementia.

Cancer Council's fundraising chief Andrew Buchanan claimed the charity was told by the 94-year-old's relatives six months after her death to expect a 'possible large bequest', according to court documents filed to the Supreme Court.

The council was told the case was 'complex' and they should contact lawyers.

Cancer Council claimed the charity was told by the 94-year-old's relatives to expect a 'possible large bequest', according to documents filed to the Supreme Court (pictured)

The council claims the dispute over the will has caused a rift in the family.

A nephew of Ms Thomson's handed over a copy of the woman's medical history which said she suffered short-term memory and needed 'constant supervision'.

Ms Thomson's condition had deteriorated so much she even needed to be directed while making sandwiches and she was unable to use her four-wheel walking frame on a regular basis, according to the court documents.

Her cause of death was cited as 'Bronchopneumonia - 4 days and Dementia of Alzheimer type - 5 years'.

Mr Jeffs' wife, Vera, said she was told by Ms Thomson to make the new will in a sworn affidavit.

'My husband and I travelled to Melbourne to care for Elizabeth shortly prior to the will being executed,' she said.

'Elizabeth told me that she wanted to make a new will. I told Elizabeth that she should go to see a solicitor.