Alexander Vinokourov's "B" sample has confirmed that he received a banned blood transfusion.
The Kazakh cyclist was expelled from this year's Tour de France when he tested positive after winning the time trial on stage 13.
Despite maintaining his innocence, the back-up sample came back positive.
The Astana team rider faces up to a two-year ban from cycling, and risks losing a year's salary under the UCI's anti-doping charter, implemented in time for this year's race.
Vinokourov insisted earlier that he would fight any blood-doping charges and maintained he has "always raced clean".
Statement
"Never before this year's Tour de France have I ever been accused of violating any doping law," Vinokourov said in a statement.
"I have been tested at least 100 times during my career. These test results simply make no sense. Given all the attention paid to doping offenses, you would have to be crazy to do what I have been accused of, and I am not crazy."
He had entered the race as one of the favourites; however his chances of victory took any early hit when he suffered a crash that damaged both his knees.
He recovered from that fall to win the time trial and also clinched a tough mountain stage in the Pyrenees. A blood transfusion from a compatible blood donor, instead of one's own blood, makes it easy to see anomalies when the blood is tested.
Transfusion
"A homologous transfusion is done with the blood of someone from the same blood group, for example A+ or even Rhesus (negative or positive)," Michel Audran, a French biophysicist and professor at Montpellier University, said.
"Thus it's different from an autotransfusion with your own blood, which remains undetectable."
Audran said the blood transfusion would increase performance by "3 to 20 per cent" because it increases the haemoglobin mass that carries oxygen to the muscles.
However, the risk for cheats is enormous.
Audran said: "If you are tested, the probability of not getting detected is feeble, 1 in 7,000."