Democrat Sen. Diane Feinstein at the last minute sent a letter to the Justice Department describing allegations of sexual misconduct involving Supreme Court nominee Brett Kavanaugh and a woman — when they were both high school students.

Feinstein, the top Democrat on the Senate Judiciary Committee, said the information came from a woman who wanted to remain anonymous, and declined to detail the letter’s contents — even to her annoyed fellow Dems.

But according to a pair of vague reports in The New York Times and The Intercept that cited multiple sources, the letter includes the allegations against the 53-year-old Trump nominee.

“I have received information from an individual concerning the nomination of Brett Kavanaugh to the Supreme Court,” Feinstein said in a statement.

“That individual strongly requested confidentiality, declined to come forward or press the matter further, and I have honored that decision. I have, however, referred the matter to federal investigative authorities.”

The FBI said it was not investigating the judge over the letter, CNN reported Thursday night.

The information came in a letter that was first sent to the office of California Democratic Rep. Anna Eshoo, who passed it along to Feinstein during the summer. It was unclear why she waited until now to pass it along to the feds.

The woman making the claims is being represented by Debra Katz, a lawyer who works with #MeToo survivors, The Intercept reported.

Joseph Abboud, a lawyer at Katz’s firm, said the firm was declining to comment.

But the White House issued a furious response — pointing the finger at Sen. Chuck Schumer in a statement.

“Senator Schumer promised to ‘oppose Judge Kavanaugh’s nomination with everything I have,’ and it appears he is delivering with this 11th hour attempt to delay his confirmation,” the statement said, while also offering a vigorous defense of Kavanaugh, whom President Trump had nominated to fill the seat vacated by retiring Justice Anthony Kennedy.

Schumer’s office replied that the senator “has not had access to the letter but believes the Judiciary Committee is handling it appropriately.”

The White House also noted that Kavanaugh, a longtime federal judge who also served in President George W. Bush’s White House, had been repeatedly vetted by the FBI.

“Throughout 25 years of public service, the Federal Bureau of Investigation has thoroughly and repeatedly vetted Judge Kavanaugh, dating back to 1993, for some of the most highly sensitive roles.”

Kavanaugh attended Georgetown Preparatory School, an all-boys’ Jesuit high school in Maryland. It was unclear what school the letter writer attended.

Judiciary Committee Chairman Chuck Grassley’s office said development would not throw a wrench into the confirmation process.

“Sen Grassley is aware of Sen Feinstein’s referral,” said George Hartmann, a Grassley spokesman.

“At this time, he has not seen the letter in question, and is respecting the request for confidentiality. There’s no plan to change the [committee’s] consideration of Judge Kavanaugh’s nomination.”

But Feinstein’s fellow Democrats want their own chance to decide whether or not the letter should be made public.