Donald Trump's grandfather was kicked out of his native Germany for failing to do his mandatory military service there, a historian has claimed.
A local council letter from 1905 informed Friedrich Trump -- who had become a United States citizen -- that he would not be granted his German citizenship back and that he had eight weeks to leave the country or be deported, German historian Roland Paul told CNN Tuesday.
He also claimed that Trump had illegally left Germany, failing to notify authorities of his plan to immigrate.
The Trump camp did not immediately respond to CNN's questions on the research.
How the Trumps reached America
According to historian Roland Paul:
Friedrich Trump was born in 1869 in the German city of Kallstadt and joined his sister. Katharina, in the US in 1885. He was first hired by a hairdresser. In 1892 he became a US citizen and changed his name to Frederick.
Trump opened up a hotel and brothel in 1894, according to the book "The Trumps: Three Generations That Built an Empire."
He then moved to the small city of Bennett and opened up the New Arctic Restaurant and Hotel that the Yukon Sun newspaper also considered a brothel. Trump returned to Kallstadt in 1901, and in 1902 married 20-year-old Elisabeth Christ.
The couple moved to New York and in 1904, their daughter was born. He and his family returned to his hometown that year and Trump applied to get his German citizenship back as his wife wanted to leave the US.
The Kallstadt council rejected his request because he had failed to do his military service and notify them of his emigration.
The findings have sparked interest as President-elect Trump vowed to crack down on illegal immigration in his election campaign.
"Trump talks against illegal immigration, so I think he should remember his own family story from time to time," Paul said.
Trump proposed a wall be built between the US and Mexico as the centerpiece of his anti-immigration drive. He has also threatened to deport undocumented migrants who have committed crimes in the US.