Former super middleweight world titleholder Lucian Bute tested positive for a banned substance following his draw against titleholder Badou Jack on April 30 at the DC Armory in Washington, D.C.
Multiple sources told ESPN.com of the failed test, results of which came to light on Thursday.
The WBC, whose title was at stake in the fight, later said it was notified by the D.C. Boxing and Wrestling Commission that Bute had tested positive for a banned substance in his postfight anti-doping test.
Bute tested positive for the substance ostarine (also called enobosarm), which is not an anabolic steroid but is said to increase stamina and recovery ability, and produce similar results that steroids would.
It has been on the World Anti-Doping Agency banned list since 2008.
Bute's team did not respond to a request from ESPN.com for comment but Jack was not happy to hear about the positive test.
"He's still couldn't beat me even using something," Jack told ESPN.com. "I won the fight. Everybody thought I won the fight. It should not have been a draw in the first place. Hopefully, it could be changed to a win."
It is likely that the result of the fight -- a majority draw in which two judges scored the bout 114-114 and one had Jack winning 117-111 -- will be changed to a no decision. Bute (32-3-1, 25 KOs) also could face a suspension and fine.
"It's cheating," Jack said. "This is the hurt business. You can die in the ring. It's bad. I like (Bute) as a person. He's a nice guy but that's not cool at all. You put your life on the line every time you step in the ring and your opponent is cheating? You can die. Anything can happen in boxing.
"I hit him with some very hard body shots and he recovered from then, which I was surprised by. For him to come back that strong in the later rounds, that's what I was thinking about (when I heard about the failed test). I thought he was an honest guy. I didn't expect that from him."
A protege of his promoter, Floyd Mayweather, Jack, 32, a native of Sweden living in Las Vegas, claimed his 168-pound world title in April 2014 with a majority decision against Anthony Dirrell. He defended it for the first time in a decision win against George Groves in September and made his second defense against Bute.
Jack (20-1-2, 12 KOs) is slated to move on to a world title unification bout against England's James DeGale (23-1, 14 KOs) in September. DeGale outpointed Rogelio "Porky" Medina in the April 30 co-feature to retain his belt.
Bute, 36, of Montreal, held a world title from 2007 to 2012 and made nine successful defenses. The fight against Jack was his second title shot in a row. He lost a tremendously exciting and close decision to DeGale in November in Quebec City, but his performance was impressive enough to earn him another shot against Jack.
Bute is the fourth high-profile fighter to fail a drug test in the last three months:
• Heavyweight contender Alexander Povetkin tested positive for the banned substance meldonium in a random test, resulting in his mandatory shot against world titleholder Deontay Wilder being canceled a week before the scheduled May 21 bout in Moscow.
• Heavyweight titlist Lucas Browne tested positive for clenbuterol after his 10th-round knockout win to claim a secondary world title against Ruslan Chagaev on March 5 in Grozny, Russia.
The result is expected to be changed to a no decision. Also, the title was returned to Chagaev and Browne was suspended for six months by the WBA, although he could face other disciplinary action.
• Last month, junior lightweight world titleholder Francisco Vargas also tested positive for clenbuterol in a random test conducted in conjunction with the lead-up to his defense against former titleholder Orlando Salido, which is scheduled to take place June 4 in Carson, California.
He claimed he ate contaminated beef at his mother's home in Mexico, where that has been an issue for several athletes.
Because Vargas had such a small amount in his system, the fight was still more than a month away, and because contaminated meat in Mexico is a legitimate issue, the California State Athletic Commission agreed to allow the fight to go on as planned with Vargas subject to even more stringent pre-fight testing.