A woman who devoted 40 years to helping her parents run the family farm in North Yorkshire has learned they have left their £1.5m estate to the RSPCA.
Dr Gill is having court papers drawn up to challenge the will
Dr Christine Gill, 57, who has been left nothing, is now taking legal action to challenge the will.
She said she had given up a career as a Leeds University lecturer to help out on the farm near the village of Potto.
A RSPCA spokeswoman said the matter would hopefully be resolved without legal proceedings.
Dr Gill said she was a young girl when she started work on the 287-acre farm and would do various jobs such as driving tractors, stacking bales and preparing grain for the crops.
After leaving university, Dr Gill returned at weekends and during holidays to help.
She and her husband Andrew bought an adjoining property in 1986.
In 1997, after the birth of her son Christopher, she said she gave up her full time job as a lecturer at Leeds University so she could look after her parents and later run the farm.
Her father John died in 1999 and then when her mother Joyce died last year, Dr Gill discovered she had been cut out of the will and the estate left to the animal charity.
"I tailored my whole life around it," she said.
"My choice of college, where I worked - it's all built around it. They had no moral right to make that will," she said.
"The farm is close to my heart, not a money settlement."
Dr Gill said the will was made before Christopher was born and that her father may have been disappointed that he did not have a male heir at the time.
But she said that Christopher, now 10, was "very keen" on the farm.
Dr Gill is now having court papers drawn up to challenge the will under the 1975 Inheritance Act and must lodge them by October 15.
Under the Act, any child who feels that they have not been adequately provided for in their parents' will can ask the court to make financial provision for them by changing the will.
Generally, such applications are only successful if the child is still financially dependent on the deceased. Self-supporting adults will find it more difficult to prove that they need that financial support.
Dr Gill has she had also been trying to negotiate with the RSPCA but said that she feared the sale of the farm would go ahead anyway.
A spokesman for the RSPCA said it hoped "that it can be resolved without the need for legal proceedings".