Lady Lucan, whose husband famously vanished more than four decades ago in the midst of a murder case, has been found dead at home.
Police forced entry to the 80-year-old's Westminster home on Tuesday afternoon after she was reported missing, the Press Association reported.
Lady Lucan was one of the last people to see her husband John Bingham, the 7th Earl of Lucan, alive before he disappeared in November 1974.
He vanished after the murdered body of Sandra Rivett, nanny to his three children, was found at their family home.
A Met Police spokesperson said that Lady Lucan, whose first name was Veronica, was found unresponsive in her home by officers.
Her death is being treated as unexplained, but is not believed to be suspicious, police said.
Her son George Bingham, the 8th Earl Lucan, told the Daily Mail: "She passed away yesterday at home, alone and apparently peacefully.
"Police were alerted by a companion to a three-day absence and made entry today."
Lady Lucan's death comes more than 40 years after her husband's disappearance following the murder of 29-year-old Rivett.
Despite being officially declared dead by the High Court in 1999, Lord Lucan has reportedly been sighted in Australia, Ireland, South Africa and New Zealand.
There have even been claims that he fled to India and lived life as a hippy called "Jungly Barry".
The same night as his disappearance, the attacker also turned on Lady Lucan, beating her severely before she managed to escape and raise the alarm at a nearby pub, the Plumbers Arms.
Lucan's car was later found abandoned and soaked in blood in Newhaven, East Sussex, and an inquest jury declared the wealthy peer the killer a year later.
Roger Bray was the first journalist on Lord Lucan's doorstep the morning after the dramatic events unfolded, and wrote one of the first newspaper reports about the mystery surrounding the man with the famous moustache.
Head barman at the in the Plumbers Arms Derrick Whitehouse, who was 44, told Bray that Lady Lucan "staggered" in and she said: "I think my neck has been broken. He tried to strangle me."
The barman said Lady Lucan was "just in a delirious state", telling Bray: "She just said 'I'm dying'. She kept going on about the children. 'My children, my children', she said. She came staggering in through the door and I gave her all the assistance I possibly could. I've only seen her in here once before."
Whitehouse told Bray that she had "various head wounds" that were "quite severe", adding: "She was covered in blood. She'd been bleeding profusely when she came in."
"But I cannot alter it, except not to forget about her – and I don't forget about her."