The worldwide hunt for the heir to the millions follows the murder of Horst "Hans" Grahlmann, who was shot in his California home last year. The trustees of the German-born businessman are trying to track down the mother of his children, a woman thought to come from London.
If she is not found, the estate, which includes gay bars, will be handed over to America's Lutheran church, a strict Protestant group.
Mr Grahlmann, 57, was shot dead in October last year at his home in Guerneville, near San Francisco, with an employee, Jason Blore, 26. Some people believe Mr Blore was the primary target.
The eccentric property magnate died intestate, and his estate passed to his 80-year-old mother. When she died, in August this year, the estate was left without an heir until a business associate recalled Mr Grahlmann talking about his marriage to an Englishwoman.
Kenneth Crutchlow, a business acquaintance of Mr Grahlmann, launched the search for the heir at a press conference in a London hotel yesterday. He said: "All we know is that he spoke of an English wife and two children. If we can track them down, then the estate will pass to them."
After the murder, an Australian-born business associate, Peter Hackett, began to unravel Mr Grahlmann's past.
The Berlin-born chef arrived in Kansas in 1959 and is thought to have met his wife shortly afterwards. He is said to have set up home in the early 1960s and had two children, possibly a son and a daughter.
The marriage soon broke down. Mr Grahlmann left home one evening, saying he needed some fresh air, and never returned. He later claimed he took exception to his wife's habit of drying her stockings on the stove in the kitchen.
He went on to build a business empire of gay bars, nightclubs and restaurants in San Francisco, Guerneville and Hawaii.
Mr Crutchlow said: "The fact that he was a chef might have made him extra- sensitive to his wife's habit, and it seems he just snapped one day. He told friends that he thought his wife and the two children returned to England shortly after he ran away, and so they may still be here, completely unaware of the huge amount of money that could be theirs - particularly since the family were relatively poor at that time."
The search for a marriage certificate in Kansas has so far failed, but private detectives are trying to trace other documents, including the birth certificates of the two children.
Any claimant of the $20m fortune will be expected to provide proof of their identity and a DNA sample.Reuse content