The probe of Brooklyn DA Ken Thompson’s funny lunch-money habits was sparked by a February 2015 story in The Post about the personal errands he assigned to members of his security detail, documents reveal.

The Department of Investigation confirmed that Thompson’s protective detail spent thousands of dollars buying him meals between January 2014 and February 2015 — and that they were reimbursed with taxpayer funds.

As a result of the findings, Thompson was fined $15,000 by the Conflicts of Interest Board for violating the city’s ethics rules.

The DOI investigation also details Thompson’s finger-pointing over the out-of-bounds practice, including blaming his predecessor, Charles Hynes.

But when asked about the prior practice, witnesses gave differing accounts as to whether that was true.

And when asked which member of the detail told him it was standard practice, Thompson couldn’t recall the name.

Thompson’s lawyer, Michele Hirshman, noted that the DA reimbursed taxpayers in full for the expenses and that he followed office policy created in spring 2014, which was dropped in 2015 after it was deemed to violate city conflicts law.