(CNN) President Donald Trump has come under fire for using the name of a famous Native American as a slur -- at an event honoring Native Americans for their service as code talkers in World War II, no less.

Trump turned to his often-used insult of "Pocahontas" to slam Sen. Elizabeth Warren, whom he claims has embellished her purported Native American heritage. Warren has said she was raised being told that she is part Native American, but has maintained that she never used this aspect of her heritage to advance her career.

Trump's repeated attacks on Warren come despite his own family's past efforts to hide their heritage. According to multiple reports from The New York Times and the Boston Globe and a biography, Trump's father repeatedly sought to conceal the fact that he was the son of German immigrants.

Fred Trump sought to pass himself off as Swedish amid anti-German sentiment sparked by World War II. According to the biography "The Trumps: Three Generations that Built an Empire" by Gwenda Blair, Fred Trump denied knowing German and did not teach it to his children.

John Walter, a Trump family historian and one of Donald Trump's cousins, said this was an effort to not offend his Jewish customers.

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