Russian runner Maria Savinova has been stripped of her 2012 Olympic gold medal for doping, putting Caster Semenya in line to become a two-time champion.
Savinova, who won the 800m title at the London Games ahead of Semenya, was also banned for four years by the Court of Arbitration for Sport.
CAS said the 31-year-old Savinova was "found to have been engaged in using doping" from July 2010 until August 2013.
In 2014, Savinova was caught in undercover footage filmed by Russian doping whistleblower Yulia Stepanova, appearing to admit to injecting testosterone and taking the banned steroid oxandrolone.
The footage helped spark a World Anti-Doping Agency investigation into Russia and led to Savinova's blood samples being re-examined.
Savinova has not raced competitively since 2013. She had been preparing for a comeback when she was filmed by Stepanova and was then suspended during the investigation.
Following further evidence of widespread drug use, the Russian track team was suspended from all international competitions in November 2015 and missed last year's Olympics.
If the International Olympic Committee decides to re-allocate the medals from the 2012 final, Semenya will add that gold medal to the one she won last year in Rio de Janeiro.
The original bronze medalist in the 2012 Olympic final, Ekaterina Poistogova of Russia, is also under investigation for doping. If she is banned, Pamela Jelimo of Kenya would be in line for silver, with bronze for Alysia Montano of the United States.
Another Russian who originally finished sixth, Elena Arzahkova, was retrospectively disqualified in 2013 over blood doping.
Semenya could also become a two-time world champion by inheriting Savinova's gold medal from 2011. Yvonne Hak of the Netherlands is in line for the 2010 European title, though Savinova keeps the 2010 world indoor title she won ahead of Britain's Jenny Meadows.
The Russian is also obliged to return at least $US156,000 in prize money from various competitions where she's now considered disqualified.
The WADA commission that investigated Russian track and field had originally recommended a lifetime ban for Savinova. She can appeal the CAS ruling within 45 days.
In the footage filmed by Stepanova, Savinova said doping was the only way to succeed in Russian sport.
"What should we do? How should it go differently? That is our system and in Russia that only works only with pharma," she said, according to a transcript produced by WADA.
"Oxandrolone is very quickly out of my body out again. It takes less than 20 days."
Savinova also said that her husband, former runner Alexei Farnosov, had used "contacts" at a drug-testing laboratory to help cover up her doping. The Moscow drug-testing laboratory was later shut down and its director testified he had covered up hundreds of failed tests by top Russian athletes.
Two top coaches who worked with Savinova - Alexei Melnikov and Vladimir Kazarin - have also faced punishment.
Melnikov was banned for life by the IAAF last year, while Kazarin is suspended awaiting the results of an investigation, though he's been accused of breaking that suspension by continuing to coach Russian runners.