Jones requested his "B" sample be tested after his "A" sample tested postive for Turinabol, a banned substance.
Jon "Bones" Jones's "B" sample tested positive for Turinabol, a banned substance, after his "A" sample also tested positive for the performance-enhancing drug after he defeated Daniel Cormier at UFC 214 on July 29.
"Mr. Jones 'B' sample has confirmed the 'A' sample findings," a spokesperson for the United States Anti-Doping Agency (USADA) told ESPN. "Importantly -- as previously stated -- due process should occur before drawing any conclusions about this matter."
Athletes who fail drug tests often request that their "B" sample, which was taken at the same time as the "A" sample, be tested. If the "B" sample does not also test positive, it casts doubt as to the legitimacy of the first test.
Jones has already had multiple issues with positive drug tests. In 2016, Jones was supposed to fight Cormier at UFC 200, but the fight was called off because Jones tested positive for performance enhancing drugs. As a result, he was suspended by a year by the USADA, and UFC 214 marked his first time back in the ring after the suspension.
Jones also tested positive for cocaine prior to UFC 182, in which he defeated Cormier in January 2015. The positive test did not become public until after the fight, and Jones later said he beat Cormier after a "week of cocaine."
Per USADA rules, Jones faces a suspension of up to four years.
Jones' camp released the following statement after the most recent failed test became public to MMAFighting.com:
"We are all at a complete loss for words right now. Jon, his trainers, his nutritionists and his entire camp have worked tirelessly and meticulously the past 12 months to avoid this exact situation. We are having the samples tested again to determine the validity or source of contamination. Jon is crushed by this news and we are doing whatever we can as a team, to support him."
ESPN reports that Jones' victory, which came by third-round knockout, will most likely be changed to a no-contest, but the UFC has not yet officially stripped Jones of his title.