Man adopted as a baby details moment he learned biological parent's identity and terrifying past

'This just doesn't happen, does it?', Neil asks, 'the chances of you being adopted and finding out that your mother is [involved] in one of the biggest murder mysteries of all time - it's unbelievable'.

Neil Berriman was given up for adoption as a baby and for more than 30 years refused to open an envelope his adoptive mother had told him about.

John Bingham, later the 7th Earl of Lucan, and Veronica Mary Duncan announce their engagement, UK, 14th October 1963. He disappeared in November 1974 after their children's nanny was found murdered in their family home (Evening Standard/Hulton Archive/Getty Images)

"You should open it. There's items in the envelope that [will give you] the answers to some questions," he recalls his mom telling him, to a BBC film crew for a new docu-series titled Lucan.

"I remember saying, 'No, mum. I'm not interested. I don't need the brown envelope.'"

Berriman was completely oblivious that his mom was at the heart of a murder mystery that gripped the world at the time, as his mom Sandra Rivett was killed at the young age of just 29 years old, while working as a nanny for John Bingham, the 7th Earl of Lucan - commonly known as Lord Lucan.

Finally, three years after Berriman's adoptive mother passed away, he opened the envelope and inside it he found his adoption certificate and a newspaper article from 1994.

The article explained how a man called Stephen Hensby was the son of Sandra Rivett.

While Berriman's adoption correspondence revealed his birth name was Gary Roger Hensby.

He said: "So Stephen - the boy from the newspaper article - must be my brother. But [the nanny] can't be connected to me because she's called Sandra Rivett.

"I read the article one last time and down [at] the bottom I then realised her name was actually Sandra Eleanor Hensby."

Neil Berriman, son of Sandra Rivett, the murdered nanny that worked for Lord Lucan (JUSTIN TALLIS/AFP via Getty Images)

Before adding: "I am the son of Sandra Eleanor Hensby - also known as the nanny murdered by Lord Lucan in 1974.

"A single letter is what I was expecting. This just doesn't happen, does it?

"The chances of you being adopted and finding out that your mother is [involved] in one of the biggest murder mysteries of all time. It's unbelievable."

At the time, in 2007, Berriman didn't know too much about the case - only knowing the basics, completely oblivious that it involved his biological mom, who he previously thought was his sister.

Sandra's murder came 33 years prior to him finding out, on November 7, 1974, on her day off from nannying Lord and Lady Lucan's children.

A police report read: "Thursdays were usually Sandra Rivett's night off, but she had not gone out that evening. At approximately 8.55pm Sandra Rivett asked Lady Lucan whether she would like a cup of tea... and went down to the basement, where the kitchen was.

"At about 9.15pm Lady Lucan went to the basement to see what was taking Sandra so long. She got to the top of the stairs that led to the basement and was surprised to see that there were no lights on.

John Bingham, later the 7th Earl of Lucan, and Veronica Mary Duncan announce their engagement, UK, 14th October 1963. He disappeared in November 1974 after their children's nanny was found murdered in their family home (Evening Standard/Hulton Archive/Getty Images)

"She shouted 'Sandra, Sandra'. Then she heard a noise from a room behind her and she was struck over the head a number of times. At this stage, she had not seen her attacker.

"She fell to the ground and started to scream. Her attacker then put his gloved fingers down her throat and told her to 'shut up'. She recognised the voice as Lord Lucan's. A struggle ensued, during which Lady Lucan bit his fingers and grabbed his genitalia."

Lady Lucan managed to convince her husband to let her wash her injuries, and when he went to use the toilet she made a run for it to the nearest pub where she reported what happened and asked someone to call the police to help save their children.

Lord Lucan absconded and managed to completely evade detection, he vanished and to this day never served justice for killing Sandra.

More than 50 years later, Lord Lucan was presumed dead in 2015, but if those assumptions are wrong, he'd turn 90 this year on December 18.

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