Jon Jones' B sample came back positive for a prohibited substance, confirming the results of his initial test dating back to his UFC 214 win over Daniel Cormier.
The drug found in Jones' system is widely reported to be Turinabol, an anabolic steroid, with the United States Anti-Doping Agency (USADA) confirming the B sample had matched the conclusions of the original findings.
Jones, who knocked out Cormier on July 29 to improve his record to 23-1, returned a positive result for the substance from a test taken a day prior to that fight, and was notified last month.
"Mr. Jones' B sample has confirmed the A sample findings," a USADA spokesperson told Omnisport.
"Importantly - as previously stated - due process should occur before drawing any conclusions about this matter."
The 30-year-old did pass a blood test in the aftermath of the bout, although Turinabol is not detected by such means.
This is Jones' second positive drug test in the UFC. He was suspended by USADA for a year after testing positive prior to a scheduled meeting with Cormier in 2016.
He blamed the first test on a tainted sexual enhancement pill and received his punishment for negligence.
Jones passed two urine tests in early July leading up to his clash with Cormier this year. If suspended again by USADA, he will likely receive a four-year suspension from the organisation, which is standard for a second offence.