The widow of Lord Lucan died from a cocktail of drink and drugs after diagnosing herself with Parkinson’s disease, an inquest was told.
Police discovered 80-year-old Lady Lucan’s body after forcing entry into her London home last year.
She was found on the dining room floor with a pill bottle under her body, Westminster Coroner’s Court heard.
A pathologist concluded she died from respiratory failure caused by barbiturates and alcohol poisoning.
Born Veronica Duncan, Lady Lucan was reported missing by a worried friend after not turning up for her regular walk, the inquest heard.
Police subsequently smashed a window to break into the two-storey terraced town house in Belgravia, central London, at around 17:30 GMT on 26 September 2017.
Lady Lucan, who was born in Uckfield, East Sussex, was worried she had developed Parkinson’s after she noticed a tremor in her right hand, lost her sense of smell, felt tired, anxious and suffered from insomnia, as well as becoming forgetful.
The hearing was told she had attended a meeting on assisted suicide the previous year and complained of having money troubles.
Notes were found in her diary on how to take her own life if she became frail and had books on assisted dying.
In one entry on 5 August last year, about six weeks before her death, she listed potential suicide items copied from four suicide books found in her house.
A later entry detailed her suspected Parkinson’s symptoms, but she had not been diagnosed by a doctor, the hearing was told.
In a written statement David Davies, who had known her for two years, said: “There was nothing in her behaviour to suggest anything was wrong.
“Although she thought she had the onset of Parkinson’s and had a tremor in her right hand and was worried she’d lost her sense of smell.
“We both discussed how to end our lives but only if we developed a degenerative or terminal illness or became reliant on other people.
“But there was nothing to suggest she was considering this and she seemed cheerful the last time I saw her.”
Coroner Dr Fiona Wilcox recorded a conclusion of suicide.