Cologne prosecutors continue doping investigations into Felix Sturm, whose secondary "b-sample" also came back positive. Sturm, a former middleweight and super-middleweight champion, gave up his belt during the probe.
The positive tests date back to this points victory for Sturm in February
A spokesman for the prosecutors' office in Cologne, Daniel Vollmert, said on Friday that German boxer Felix Sturm had also failed a doping re-test of his secondary "b-sample" taken before his February 20 victory against Russia's Fedor Chudinov.
"The results of the b-test are also positive. The preliminary suspicion has been confirmed," Vollmert said.
First accused of wrongdoing in April, when he vehemently denied the allegations,Sturm faces possible charges under Germany's law against doping in sport - which can carry a fine or a jail sentence of up to three years.
He tested positive for a substance called hydroxy-stanozolol, a type of steroid popular among bodybuilders.
Sturm won February's fight, a rematch against Chudinov in which he reclaimed the WBA super-middleweight title, on points; although some observers questioned the judges' decision to award the fight to the home favorite in Oberhausen. It was Sturm, not Chudinov, sporting severe facial wounds after the bout.
Sturm got the points decision in February despite looking rather the worse for wear after 12 rounds
On October 5, the boxer's management announced that Sturm had ceded his WBA belt - albeit saying he did so because of an injury to his elbow.
After this, the boxing bodies chose not to suspend or ban the 37-year-old, prompting German authorities to also look the other way.
"Because the world federation has not opened proceedings against Sturm, he also will not face the threat of consequences from us," Thomas Putz, the head of Germany's BDB boxing federation, told sports news agency SID. According to the BDB's own statutes, the maximum punishment it could level against Sturm would be a one-year ban.
Born in Leverkusen as Adnan Catic to parents of Bosnian descent, Sturm has moved to Bosnia during the course of the investigations.