Former first lady Michelle Obama in her upcoming book "Becoming" said she would "never forgive" President Donald Trump for promoting the false birther conspiracy.

During the 2012 US presidential election, Trump floated the racist conspiracy theory that President Barack Obama was not a US citizen, and touted the demonstrably false claim that Obama's birth certificate was not real.

Mrs. Obama called the conspiracy "crazy and mean-spirited," and said it endangered her family.

"What if someone with an unstable mind loaded a gun and drove to Washington," she wrote in her book, according to The Washington Post. "What if that person went looking for our girls? Donald Trump, with his loud and reckless innuendos, was putting my family's safety at risk."

RELATED: Trump answered to Michelle Obama - 'I'll never forgive Barack Obama'

Former first lady Michelle Obama in her upcoming book laid out her most damning statement against President Donald Trump, who she said promoted the "dangerous" birther conspiracy that could have endangered her family's safety.

"The whole [birther] thing was crazy and mean-spirited, of course, its underlying bigotry and xenophobia hardly concealed," Obama wrote in her memoir, according to a Washington Post review. "But it was also dangerous, deliberately meant to stir up the wingnuts and kooks."

For years, even prior to the 2012 US presidential election, Trump fueled the racist conspiracy theory that questioned the authenticity of President Barack Obama's birth certificate and his citizenship.

"He doesn't have a birth certificate, or if he does, there's something on that certificate that is very bad for him," Trump said during an interview with Fox News host Laura Ingraham in 2011.

Obama added that she would "never forgive" Trump for promoting the birther movement.

"What if someone with an unstable mind loaded a gun and drove to Washington," she added. "What if that person went looking for our girls? Donald Trump, with his loud and reckless innuendos, was putting my family's safety at risk. And for this I'd never forgive him."

Obama eventually released his longform birth certificate. In September 2016, Trump relented and admitted Obama was born in the country, but added an unverifiable claim that his then-Democratic presidential opponent Hillary Clinton was to blame for promoting the conspiracy theory.

"President Barack Obama was born in the United States," Trump said during a press conference at the time. "Period. Now we all want to get back to making America strong and great again."

"Hillary Clinton and her campaign of 2008 started the birther controversy," Trump added. "I finished it. I finished it. You know what I mean."

Obama's memoir "Becoming" releases on November 13.

See also: Future policy of US after elections