James Prichard, Dame Agatha Christie's great-grandson, has revealed the author's "traumatising" second job that inspired her ground-breaking novels. Fifty years after the Queen of Crime's passing, the world still can't get enough of her brilliance. Her latest Netflix mystery, Seven Dials, is a ratings hit, a Miss Marple reboot is in the works, and her award-winning play, The Mousetrap, remains a West End hit 73 years after its debut.

None of this surprises the writer's great-grandson, who became chairman and chief executive of her estate in 2010. "We're probably selling more books now than we have for a very long time," he chuckled with obvious delight. To mark the milestone moment, The Christie Trust has teamed up with Wooga's 1920s-set mystery game June's Journey, which sees Hercule Poirot appearing in the game as part of a three-month event.

But one thing that may surprise fans is the star's surprising first job before she became an internationally adored crime writer. Born to a prosperous family in Torquay, Devon, she was homeschooled by her father, Frederick, for much of her childhood and taught herself to read by the age of five.

Before the author published her first novel in 1920, she also boasted a surprising first job as a pharmacist when the First World War began in 1914. Understandably, her world turned upside down during the war, which led the author to abandon her work to help Britain stay afloat.

Speaking exclusively to Express.co.uk, Prichard revealed to us: "Like a lot of young women at that time, she volunteered and worked as a nurse throughout the First World War. That was presumably quite a traumatic experience where she regularly saw fairly unpleasant things.

"But she became a pharmacist, and she learned about drugs and medicines, which obviously crept into her writing. Her experience with drugs, with poisons, and her knowledge of how they worked and how you could disguise them, a lot of it comes from that experience as a nurse during the First World War."

Just two years after the conflict ended, Christie published her first novel, The Mysterious Affair at Styles, where she introduced one of her most famous literary characters, Hercule Poirot.

Prichard considers the fastidious Belgian detective her greatest creation, as he revealed the source of the iconic character's inspiration. "I don't know where Poirot came from, but there's a story of her seeing Belgian refugees by the side of a bus stop in Torquay, and that's probably true, but exactly where that particular person came from was really in her head."

Another one of her keen passions, which bled into her work, was her love for travelling. In 1922, Agatha and her first husband, Archie, embarked on a 10-month grand tour of the British Empire.

During their retreat, Agatha learnt and perfected the craft of surfing, and is widely believed to be the first Western woman to learn to surf standing up in South Africa. This is thought to have inspired the book, The Man in the Brown Suit, which featured a protagonist who travels to South Africa and tries - and fails - to surf.

After marrying her second husband, Max Mallowan, she spent months every year living in the Middle East on excavation sites as a keen archaeologist. During her annual retreats, she became a regular on the Orient Express, which travelled between London and Baghdad.

Her now-infamous book, Murder on the Orient Express, was inspired by a real-life incident in which her train was stuck in a blizzard for 24 hours. She also drew similar inspiration for her books Death on the Nile, Murder in Mesopotamia, and Appointment with Death.

Despite being her most famous detective, Christie expressed dislike for the moustached detective frequently over the years. Today, James waves this away as fickleness. “There are quotes from her talking about her frustration with Poirot at various times, but if you spoke to any writer, they’d say they get frustrated with returning characters at some point.”