President Donald Trump‘s nephew says he doesn’t believe the stories his uncle is telling ahead of 9/11’s 25th anniversary … insisting Trump never sent workers to help in the aftermath of the attack and that his U.S. steel story is a total fabrication.

Fred Trump took to social media on Tuesday to address claims President Trump has pushed in the days before September 11 … starting with his assertion that he sent many workers to help at Ground Zero after the attack.

Fred says the claim that President Trump brought workers to help at the site “so offends me that I need to speak out.” He denies the idea that President Trump was building a skyscraper in Manhattan at the time — the Trump World Tower opened months before the attack.

He says the “only crew he claimed to bring to the site would have been secretarial and accounting employees from Trump Tower I knew many of them, and pretty sure they were not capable physically to help (if they could, I am sure they would try).”

As for Trump’s assertion that two firefighters carried him away from the U.S. Steel Building after 9/11 for fear the building might collapse … Fred says this just can’t be true.

He says a brother of a partner of his was an engineer who was called to perform an immediate inspection … and, while he notes people were originally concerned, it was not cleared because it was “creaking and ready to fall.”

ICYMI … Trump said Tuesday he was dragged away from the U.S. Steel building right after 9/11 — though he was in his office calling into a local TV show multiple miles uptown at the time of the attack.

He could’ve meant in the days after the attack — in fact, a federal building near U.S. Steel was evacuated on September 12 … but it’s worth noting there are no contemporaneous news reports that corroborate his story.

Still, Trump took to Truth Social Tuesday night to insist he’s telling the truth about all his 9/11 claims.

Fred and the president aren’t exactly close … with the former criticizing the latter in his 2024 memoir “All in the Family: The Trumps and How We Got This Way.” Fred’s father is President Trump’s older brother, also named Fred, who died in 1981 of a heart attack.