Oscar Pistorius has been found guilty of murder.
Oscar Pistorius in court
The 29-year-old Olympian was found guilty of culpable homicide and reckless endangerment by a South African court last year after killing his girlfriend Reeva Steenkamp in February 2013, when her shot four times through a locked toilet door.
However, an appeals court has now overturned the original verdict, meaning he will have to return to court to be re-sentenced for murder.
Justice Eric Leach said: "As a matter of common sense at the time the fatal shots were fired, the possibility of the death of the person behind the door was clearly an obvious result.
"And in firing not one but four shots, such a result became even more likely."
The Supreme Court of Appeal concluded that the lower court did not correctly apply the rule of whether the gold medal-winning athlete knew that a death would be a likely result of his actions.
Pistorius - who became the first double leg amputee to participate in the Olympics in London in 2012 - is currently under house arrest after spending one year of his original five-year sentence in jail.
In South Africa, however, the minimum sentence for murder is 15 years, although judges are able to apply some discretion.
Pistorius is now certain to head back to prison, because the South African legal system does not allow for someone to be placed under house arrest for more than five years.
Responding to the verdict, Pistorius' family said their lawyers are studying the finding and will advise them on "options going forward".
Tagged in Oscar Pistorius Reeva Steenkamp