A bid to obtain a death certificate for Lord Lucan faces a legal objection from the son of the Earl's murdered nanny.
The seventh Earl of Lucan disappeared after Sandra Rivett, nanny to his three children, was found murdered at the family home at 46 Lower Belgrave Street, central London, on November 7 1974.
George Bingham, his son and heir, applied to have his father declared "presumed dead" so he can inherit the title as 8th Earl.
He said the move would provide "closure" four decades after his father vanished from the family home.
A period of 21 days for any objections to be raised to the application passed on Friday, but Miss Rivett's son, Neil Berriman, 47, has lodged a last-minute challenge with the High Court.
He told the Daily Mail: "I don't know if Lord Lucan is alive or not - but I want justice. There have been too many cover-ups already and he should not be declared dead. If Lord Lucan is still alive, he should be prosecuted."
The application for a death certificate was "very, very insensitive" and one should only be issued when the "truth comes out" about his mother's death, he added.
Mr Bingham placed a public notice in an independent newspaper in the capital, seeking to put an end to years of speculation about Lord Lucan's fate.
Even though he was officially declared dead by the High Court in 1999, there have been reported sightings in Australia, Ireland, South Africa and New Zealand, and even claims that he fled to India and lived life as a hippy called "Jungly Barry".
On the night of his disappearance the nanny's attacker also turned on Mr Bingham's mother Lady Lucan, beating her severely before she managed to escape and raise the alarm at a nearby pub.
Lord Lucan's car was found abandoned and soaked in blood in Newhaven, East Sussex, and an inquest jury declared the wealthy peer the killer a year later.
Mr Bingham, who was a child when his father disappeared, told West End Extra that he was applying to the High Court under the Presumption of Death Act, which came into effect a year ago.
He said the 1999 declaration had not proved death "for all purposes" and the new law allows for a "more complete process".
The Presumption of Death Act was the result of a campaign supported by relatives of high-profile missing people including chef Claudia Lawrence, who disappeared in York in 2009, and Manic Street Preachers guitarist Richey Edwards, who went missing in 1995.