Lady Anne Glenconner plotted to kill Adolf Hitler with "fluff from the carpet [and] muddy water".
The 90-year-old socialite - who was a Lady-in-Waiting to the late Princess Margaret - recalled how she and her sister were convinced the Nazi leader's allies were moving to her ancestrial home so came up with a plan to serve him a "poisonous drink" filled with every "disgusting" thing they could think of.
She told You magazine: "When we were children, my sister Carey and I plotted to kill Hitler with a poisonous drink.
"We had been sent from our home, Holkham Hall in Norfolk, up to Scotland because Hitler was meant to invade along the coasts.
"Hitler and his cohorts had all chosen a stately home in England to live in, and we were certain that Hermann Goring had picked Holkham.
"Carey and I thought, 'We'll get back to Holkham some time and we'll meet Hitler there - he's bound to come and see Goring.
"So we planned to kill him! We had a jar in which we put every disgusting thing we could; bits of food, fluff from the carpet, muddy water.
"It used to smell rather, so we tucked it away from our governess under our beds."
But the 'Whatever Next?' writer admitted she and her sister had given no thought to what would happen if their unlikely plan failed.
She added: "Anyway, we had every intention of going to Holkham with this drink and saying to Hitler, 'Oh lovely to see you Mr. Hitler, we've been saving this delicious drink for you!'
"We were absolutely determined we were going to kill him.
"We hadn't thought about what was going to happen afterwards. We hadn't got that far."