Lord Lucan, who is also believed to have escaped to India and lived a "Jungle Barry" in Goa - among many conspiracy theories linked with his disappearance in 1974 - was finally granted a death certificate under the UK's Presumption of Death Act which came into effect in 2014.
The court application had been made by his son, George Bingham, so he could inherit his father's title as 8th Earl of Lucan. The title could not have passed on until a death certificate was issued.
"I am very happy with the judgment of the court in this matter. It has been a very long time coming," George Bingham said outside the court.
Lucan had disappeared after Sandra Rivett, nanny to his three children, was found murdered on November 7, 1974.
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Bingham's application for a death certificate had faced opposition from Rivett's son, Neil Berriman.
However, that opposition was withdrawn giving way to today's decision, which Berriman described as "closure".
The mystery of the wealthy peer's vanishing act has triggered years of speculation.
Even though he was officially declared dead in 1999, there have been reported sightings in Australia, Ireland, South Africa and New Zealand, besides India.
There is one theory that he committed suicide by drowning in the English Channel soon after his disappearance.
Lucan would be 81 if he were still alive today.