The story is shocking and appears unbelievable at first. But it comes from none other than the family biographer of the Trumps – Gwenda Blair.

In her book: The Trumps: Three Generations of Builders and a Presidential Candidate, the author traced the journey of the now most powerful family in the world from its humble beginning to its entry into the White House. The journey began with sleaze, tax evasion and prostitution.

According to the author, Donald Trump’s grandfather was born as Friedrich Drumpf in Germany. But in 1885 he left for the USA and “stepped off a boat in lower Manhattan with a single suitcase. Only sixteen years old, he had left a note for his widowed mother on the kitchen table back in Kallstadt, a village in south western Germany. He didn’t want to work in the family vineyard or get a job as a barber, for which he’d been trained. He wanted to be rich and America was the place to do it.”

“Friedrich wasted no time and he did it by pushing the behavorial boundaries of his time,” Blair writes. By the early 1890s he learnt English, became a naturalized US citizen, changed the spelling of his name to the more American-sounding Frederick Trump and made his way to Seattle – a wide-open city filled with single, rootless newcomers who’d arrived expecting to make their fortunes but found themselves facing the same uncertain economic prospects they’d wanted to leave behind.”

Trump soon headed for a prime location, the city’s red-light district, known as the Lava Beds. There he leased a tiny storefront restaurant named the Poodle Dog, which had a kitchen and a bar and advertised “private rooms for ladies”–code for prostitutes. “It would allow the resourceful Trump, who renamed it the Dairy Restaurant, to offer the restless, frustrated public some right-now satisfaction in the form of food, booze and easily available sex.”

When the Klondike gold rush began in 1896, around 100,000 miners headed for the Yukon in north-west Canada – and Trump went with them. He opened the New Arctic Restaurant and Hotel in the town of Bennett, actually a ­cluster of tents on the Dead Horse Trail.

Money rolled in and Trump swapped his canvas eatery for a two-story building. It offered meals of caribou and horse meat – with sex ­available aplenty. He added salmon, duck, grouse, goose, swan, goat, sheep, rabbit and squirrel to the menu. And customers could enjoy fresh fruit – red currants, ­raspberries, strawberries, blueberries, blackberries, and cranberries. Prospectors could settle their bills in gold dust or nuggets. A set of scales sat on the bar for the purpose.

Trump built cubicles draped in heavy curtains, where his girls could entertain clients in ­privacy. But by 1901 things were ­getting too hot as the Canadian Mounties began cracking down on prostitution, gambling and illegal booze. He next opened a round-the-clock saloon in the railroad town of Whitehorse, where he served round 3,000 meals a day.

Adequately rich, Trump then returned to Germany and married his former neighbour Elizabeth Christ. He planned to settle down – but the German authorities had other ideas. Trump had avoided military service when he ­emigrated. There was also the not ­inconsiderable matter of tax he had failed to pay. His ­repatriation application was turned down and he was sent back to America with his wife.

The Guardian reported on Tuesday that a historian discovered the royal decree issued to Donald Trump’s grandfather ordering him to leave Germany and never come back. The decree orders the “American citizen and pensioner Friedrich Trump to leave the area at the very latest on 1 May … or else expect to be deported”.

In the USA, a son, Fred, was born in 1905 who became Donald’s father. Grandpa Friedrich died in the Spanish flu epidemic of 1918 at the age of 49. “He left the equivalent of £400,000 in today’s money. His widow and son invested it in property and built a ­£300million empire which was the foundation of the present day Trump’s fortune,” says Daily Mirror.

According to biographer Gwenda Blair, the father and grandfather of Donald Trump were “people who would do anything to get ahead and win…They are enormously tenacious, never give up and are willing to push the ­envelope, bend the rules and find the loopholes.”